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A critical Analysis of the ICJ’s Identification of Customary International Law in the 2023 Judgment of Nicaragua v. Colombia

Published online by Cambridge University Press:  22 May 2025

Lingjie KONG Open the ORCID record for Lingjie KONG [Opens in a new window]  and
Long CHEN
Lingjie KONG*
Affiliation:
Professor of international law at China Institute of Boundary and Ocean Studies, Wuhan University, Wuhan, China
Long CHEN
Affiliation:
LLM in international law at China Institute of Boundary and Ocean Studies, Wuhan University, Wuhan, China
*
Corresponding author: Lingjie Kong; Email: konglingjie@whu.edu.cn
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Abstract

In the 2023 judgment of Nicaragua v. Colombia, the International Court of Justice ruled that, under customary international law, a State’s entitlement to a continental shelf beyond 200 nautical miles from its baselines is not permitted to extend within 200 nautical miles from the baselines of another State. In identifying this customary rule, the Court did not apply the two-element approach. The state practice relied upon by the Court to identify the general practice is not sufficiently widespread, representative, or consistent. The opinio juris is inferred from such state practice, which is not necessarily driven by a sense of legal obligation. The Court’s assertion of the customary rule constitutes, in effect, a rewriting of the relevant provisions of the United Nations Convention on the Law of the Sea, amounting to a legislative exercise.

Keywords

customary international lawextended continental shelfNicaragua v. Colombiathe International Court of Justice

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Type
Article
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Asian Journal of International Law , Volume 15 , Issue 2 , July 2025 , pp. 306 - 324
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of The Asian Society for International Law.

On 13 July 2023, the International Court of Justice (ICJ) delivered its final judgment in the Case concerning the Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Coast of Nicaragua (hereinafter, Nicaragua v. Colombia).Footnote 1 The Court held that, under customary international law (“CIL”), a state’s entitlement to the continental shelf beyond 200 nautical miles from its baselines may not extend within 200 nautical miles from the baselines of another state. The Court thus concluded that there were no overlapping rights to the continental shelf between the parties, that a delimitation was not required, and that Nicaragua’s request for delimitation must be rejected.Footnote 2 This unexpected decision also marked the end of Nicaragua’s legal proceedings against Colombia before the ICJ.Footnote 3

This case is a follow-up of the Territorial and Maritime Disputes case initiated by Nicaragua in 2001.Footnote 4 In its 2012 judgment, the Court resolved the dispute concerning sovereignty over certain islands and the delimitation of the exclusive economic zone (“EEZ”) and continental shelf within 200 nautical miles between the parties. In response to Nicaragua’s request for the delimitation of its continental shelf beyond 200 nautical miles, the Court held that the delimitation of Nicaragua’s extended continental shelf (“ECS”) was subject to the submission by that country of information on the limits to the Commission on the Limits of the Continental Shelf (“CLCS”) in accordance with Article 76(8) of the United Nations Convention on the Law of the Sea (“UNCLOS”). In consideration of the fact that Nicaragua had provided only preliminary information to the CLCS, the Court determined that it was not in a position to uphold Nicaragua’s request for delimitation.Footnote 5 On 24 June 2013, Nicaragua made its full submission to the CLCS,Footnote 6 and subsequently requested the ICJ to effect a delimitation of its continental shelf beyond the 200 nautical miles in relation to the continental shelf of Colombia.Footnote 7 On 17 March 2016, the Court delivered its judgment on preliminary objections to jurisdiction, determining that it had jurisdiction over the case and that Nicaragua’s request for delimitation was admissible.Footnote 8 It is noteworthy that it was not until six years later that the Court, by an order dated 4 October 2022, specified that the parties would present their views at the oral hearing on the following two legal questions:

  1. (1) Under customary international law, may a State’s entitlement to a continental shelf beyond 200 nautical miles from the baselines from which the breadth of its territorial sea is measured extend within 200 nautical miles from the baselines of another State?

  2. (2) What are the criteria under customary international law for the determination of the limit of the continental shelf beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured and, in this regard, do paragraphs 2 to 6 of Article 76 of the United Nations Convention on the Law of the Sea reflect customary international law?Footnote 9

The most notable aspect of the 2023 judgment is paragraph 77, in which the Court identifies the CIL as the sole legal ground for its final ruling. In order to facilitate a comprehensive and rigorous examination of the Court’s identification of CIL, it is necessary to provide a full citation of this paragraph:

The Court notes that, in practice, the vast majority of States parties to the Convention that have made submissions to the CLCS have chosen not to assert, therein, outer limits of their extended continental shelf within 200 nautical miles of the baselines of another State. The Court considers that the practice of States before the CLCS is indicative of opinio juris, even if such practice may have been motivated in part by considerations other than a sense of legal obligation. Furthermore, the Court is aware of only a small number of States that have asserted in their submissions a right to an extended continental shelf encroaching on maritime areas within 200 nautical miles of other States, and in those instances the States concerned have objected to those submissions. Among the small number of coastal States that are not States parties to the Convention, the Court is not aware of any that has claimed an extended continental shelf that extends within 200 nautical miles from the baselines of another State. Taken as a whole, the practice of States may be considered sufficiently widespread and uniform for the purpose of the identification of customary international law. In addition, given its extent over a long period of time, this state practice may be seen as an expression of opinio juris, which is a constitutive element of customary international law. Indeed, this element may be demonstrated “by induction based on the analysis of a sufficiently extensive and convincing practice” (Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada/United States of America), Judgment, I.C.J. Reports 1984, p. 299, para. 111).Footnote 10

In relation to the Court’s identification of CIL and particularly this paragraph of the judgment, Judges Tomka, Robinson, Charlesworth, and Skotnikov have attached dissenting opinions, while Judge Xue Hanqin has appended a separate opinion.Footnote 11 Judge Tomka even inquired why the Court had not simply dismissed Nicaragua’s application in the 2012 or 2016 judgments if it had considered that there existed such a customary rule.Footnote 12 This paragraph of the judgment has also been the subject of considerable criticism from a number of scholars.Footnote 13 Among other things, the Court has been accused of failing to accord sufficient weight to contradictory state practice, of merely identifying opinio juris without examining the varied motives behind the state practice, and of adopting an approach to identifying CIL that departs substantially from its own judicial practice.Footnote 14

Indeed, the question of whether international law permits a state to extend its ECS within 200 nautical miles from the baselines of another state has become a significant issue in recent years. However, as the Court explicitly recognized in the present case, Article 76 of the UNCLOS, which provides for the definition of the continental shelf, the entitlement thereto, its outer limits, and the procedural and substantive rules for its delineation, does not explicitly address this question. Nor can a clear answer be derived from other relevant provisions of the Convention.Footnote 15 Moreover, there is no evidence to suggest that states had accorded this issue particular attention during the Third United Nations Conference on the Law of the Sea.Footnote 16 International tribunals, including the ICJ, have addressed relevant issues in the Bay of Bengal, Somalia v. Kenya, and Mauritius v. Maldives cases. Nevertheless, the judicial bodies have thus far declined to provide a definitive answer to the question.Footnote 17

The ICJ’s judgment is legally binding only in relation to the parties to the specific case.Footnote 18 However, the Court’s definitive ruling on the CIL will undoubtedly have significant implications for the regime of the continental shelf and the rights of all states, most notably those of the coastal states, as set forth in the UNCLOS.Footnote 19 This article will present a critical analysis of the Court’s identification of CIL in Nicaragua v. Colombia. In particular, the approach of the Court, as set out in paragraph 77 of the judgment, is considered in the light of the relevant conclusions in the Draft Conclusions on the Identification of Customary International Law (Draft Conclusions) adopted by the International Law Commission (“ILC”), as well as the settled international jurisprudence. The Draft Conclusions were adopted by the ILC in August 2018, following a second and final reading. The set comprises sixteen draft conclusions with commentaries, which were endorsed by the UN General Assembly in its resolution 73/203. It should be noted that such a resolution is not endowed with binding force or any legal effect by the Charter of the United Nations.Footnote 20 Nevertheless, the ILC’s output appears to have already established itself as a basic reference for consideration of the matter.Footnote 21 Part I of the article demonstrates that, despite purporting to adhere to the two-element approach, the Court has not truly implemented it. Parts II and Ⅲ, respectively, examine the deficiencies in the Court’s identification of the general practice and the opinio juris. Finally, Part IV concludes.

I. Failure of the ICJ to Apply the Two-Element Approach

In paragraph 46 of the 2023 Nicaragua v. Colombia judgment, the ICJ referenced the Court’s seminal statement on the identification of CIL, as articulated in Libya v. Malta: “the material of customary international law is to be looked for primarily in the actual practice and opinio juris of States”.Footnote 22 This is, at the very least, an indication that the Court has paid lip service to the two-element approach. In paragraph 77 of the judgment, the Court found that the practice was sufficiently widespread, representative, and consistent to constitute a general practice. In addition, the Court considered this state practice to be an expression of opinio juris. The Court did not satisfy the two-element approach, which requires the identification of the two elements on an independent basis.

A. The Two-Element Approach for Identifying Customary International Law

The two-element approach, which is essentially an inductive approach, is considered to be the fundamental methodology for identifying CIL.Footnote 23 Article 38(1)(b) of the Statute of the ICJ defines CIL as “international custom, as evidence of a general practice accepted as law”.Footnote 24 This definition clearly identifies general practice and opinio juris as the two indispensable constituent elements of CIL.Footnote 25 Similarly, Conclusion 2 of Part Two on the “Basic approach” of the Draft Conclusions is unambiguous in stating that “To determine the existence and content of a customary international law, it is necessary to ascertain whether there is a general practice that is accepted as law (opinio juris)”.Footnote 26 Furthermore, the two-element approach has also been consistently upheld by the ICJ in a large number of cases. It is seen as a fundamental requirement for maintaining the coherence and unity of positive international law.Footnote 27 In this regard, Michael Wood, the Special Rapporteur on the identification of CIL, has stated that alternative approaches to the formation and identification of CIL are, essentially, policy proposals.Footnote 28 Without practice, CIL would be a misnomer, and without opinio juris, the difference between international custom and simple regularity of conduct or other non-legal rules of conduct would disappear.Footnote 29 The two-element approach is distinguished from other approaches in terms of its operationality, predictability, and stability. Moreover, it provides an analytical framework under which claims about custom can be made, and it constrains the range of arguments that can be plausibly made either to establish or to dismantle a putative customary rule.Footnote 30

B. The ICJ has not Really Applied the Two-element Approach in Nicaragua v. Colombia

In Nicaragua v. Colombia, the ICJ did not adhere to the two-element approach in identifying the CIL.

First, the test should be focused on whether there is a general practice that is accepted as law.Footnote 31 In Nicaragua v. Colombia, however, the ICJ asserted the existence of the two constituent elements of CIL in a six-sentence dictum. The Court invoked Libya v. Malta to illustrate the relationship between the EEZ and the continental shelf. It then ruled out the need for an in-depth discussion of the phenomenon of “grey area” in maritime delimitation. Next, it went on to explain that the purpose of the UNCLOS in setting out the substantive and procedural conditions for the establishment of the outer limits of the ECS is to protect against encroachment on the Area. Furthermore, the Court explained why payments or contributions with respect to the exploitation of the ECS are required under Article 82(1) of the Convention.Footnote 32 While these issues may have some bearing upon the identification of the CIL in question, they do not provide a means of identifying the two components of the CIL. As regards the identification of the general practice, the Court was aware of the debate between the parties as to the probative value of the relevant state practice.Footnote 33 However, no specific state practice was referenced or evaluated, nor was any analysis or evaluation provided of significant state practices that were contradictory, inconsistent, or inconclusive. In the context of opinio juris, the Court merely stated that such state practice could be considered as an expression of opinio juris.Footnote 34 The Court did not provide any further evidence of the existence of opinio juris. In this context, Judge Tomka, in his dissenting opinion, criticized the Court for its perceived failure to fully investigate the underlying motives of the states in question. Furthermore, the Court’s inference of opinio juris was a “perilous leap to make”.Footnote 35

Second, the Court’s evaluation of the two constituent elements of CIL does not align with the fundamental requirement of the two-element approach. In this regard, Conclusion 3 of the Draft Conclusions suggests that each of the two constituent elements should be evaluated and identified separately.Footnote 36 The ILC has emphasized that the existence of one element may not be deduced merely from the existence of the other, and that a separate inquiry needs to be carried out for each.Footnote 37 In the present case, however, the Court inferred opinio juris from state practice completely.Footnote 38 The Court did not address the considerable ambiguity surrounding the motivations behind the states’ self-constraint actions. Indeed, the parties have presented opposing views regarding the existence of opinio juris. Nicaragua has maintained that the self-constraint actions of certain states in their CLCS submissions were driven by factors other than a sense of legal obligation. In contrast, Colombia has advanced the position that, in specific circumstances, the conduct of a state may serve as an indicator of opinio juris.Footnote 39 It is perplexing that the Court chose to disregard this contentious point.

Third, the approach adopted by the ICJ in the present case represents a notable departure from its previous practice. To illustrate, in State Immunity, the Court indicated the facts from which state practice and opinio juris should be primarily sought. After considering the adoption of international conventions, national legislation, and the judgments of national courts, the Court concluded that CIL continued to require that a state be accorded immunity in proceedings for torts allegedly committed on the territory of another state by its armed forces and other organs of state in the course of conducting an armed conflict.Footnote 40 In contrast, the Court’s approach in the present case appears to align more closely with the “single-element theory”.Footnote 41

In conclusion, the two-element approach is widely acknowledged as the most fundamental and reliable methodology for identifying CIL. In the present case, the Court reaffirmed its intention to adhere to that approach. However, in practice, the Court did not identify the existence of a general practice and opinio juris as two distinct elements. In particular, the Court inferred the existence of opinio juris from the state practice, which did not necessarily reflect a sense of legal obligation on the part of the states in question.

II. Deficiencies in the ICJ’s Identification of General Practice

The fundamental element of CIL is the existence of a general practice, which is defined as “the practice of States that contributes to the formation, or expression, of rules of customary international law”.Footnote 42 State practice can be manifested in a variety of forms, including diplomatic acts and correspondence, conduct in connection with treaties, legislative and administrative conduct, decisions of national courts and so on.Footnote 43 This objective constituent element of CIL is the primary factor to be considered, given that the conduct of states is often more readily investigated and determined than opinio juris.Footnote 44 In general, the evaluation of general practice should be conducted in its entirety, with a focus on whether the practice in question has a general character. In particular, the concept of generality in state practice implies that the practice must be sufficiently widespread, representative, and consistent.Footnote 45

In Nicaragua v. Colombia, the Court primarily relied on the submissions made by several states to the CLCS regarding the outer limits of their ECS. In the 55 submissions made by 43 states, the states in question could have asserted an ECS within 200 nautical miles from the baselines of another state. A total of 39 states in 51 submissions have restricted their claims. In light of this evidence, the Court identified a general practice. Nevertheless, as will be demonstrated in the subsequent section, the state practice in question fails to meet the requisite criteria of being sufficiently widespread, representative, or consistent.

A. The State Practice is not Sufficiently Widespread

With regard to the criteria for evaluating the extensiveness of state practice, there is no precise requirement in international law regarding the number and geographical distribution of such practice.Footnote 46 Rather, the standard of being sufficiently widespread depends on the nature and specific application of the customary rule in question.Footnote 47 In this regard, Conclusion 3 of the Draft Conclusions and the commentary thereto place significant emphasis on the necessity of clarity regarding the subject matter regulated by the rule in question, as well as the nature of the rule itself.Footnote 48 This is because these factors have an impact on the application of the two-element approach by the Court.Footnote 49 In Nicaragua v. Colombia, the Court was tasked with identifying a customary rule that has significant implications for the continental shelf regime. The right of a coastal state to the continental shelf is based on the fundamental principle that land dominates the sea.Footnote 50 This is an inherent and ab initio right that does not require any form of declaration.Footnote 51 It is evident that the existence of this customary rule has significant implications for the rights and interests of all states, particularly those of the coastal states.Footnote 52 It thus follows that a customary rule of such a general applicability requires a higher standard regarding the extensiveness of state practice.Footnote 53 In North Sea Continental Shelf, Judge Ammoun, in his separate opinion, observed that while the state practice invoked by the parties was significant, the number of such practices represented only a minor portion of the practice of the international community. These practices, which represent only approximately half of the relevant practices of the international community, cannot be considered an objective element required by a CIL.Footnote 54 In the present case, although there were 51 submissions to the CLCS made by 39 states, the evidence was limited in both quantity and form.

Similarly, in Fisheries Jurisdiction, the Court undertook a comprehensive examination of the views of states at relevant international conferences, and bilateral and multilateral international agreements, particularly agreements with a large number of state contracting parties, in order to determine whether CIL conferred a preferential right to the coastal states.Footnote 55 In contrast, in the present case, apart from the four counter-examples mentioned by Nicaragua in its oral pleadings, namely China, Nicaragua, the Republic of Korea, and Somalia, the Court has failed to acknowledge the contradictory practice in the CLCS submissions. Among the practices invoked by Nicaragua and the judges, two are worthy of particular mention.Footnote 56

In the first instance, France made a submission to the CLCS in 2014 in respect of the continental shelf of the French archipelago of Saint-Pierre-et-Miquelon. A comparison of the schematic illustration of “Fixed points of the outer limit of the continental shelf of Saint-Pierre-et-Miquelon” therein with the schematic illustration of “Outer limits of the continental shelf in the Nova Scotia Area” contained in the submission made by Canada in 2013 in respect of the continental shelf in the Atlantic Ocean reveals that a portion of the continental shelf claimed by France extends into 200 nautical miles from Canada’s baselines.Footnote 57 In the second instance, in 2012, Gabon made its submissions to the Commission in respect of the outer limits of the continental shelf beyond 200 nautical miles from the baselines.Footnote 58 In 2021, the Republic of Congo presented communications to the CLCS, which states that it

has reservations in respect of the submission of the Gabonese Republic, owing to the possible overlap of the southern part of the area to which the submission refers with the maritime areas of the Republic of the Congo and the area of the extension of the continental shelf beyond 200 miles identified by the Republic of the Congo in its preliminary information submitted to the Secretary-General of the United Nations on 12 March 2009.Footnote 59

Although the Republic of Congo has not made its own submissions, the statement has employed the phrase “maritime areas” in addition to “the area of the extension of the continental shelf beyond 200 miles identified by the Republic of the Congo”. This indicates that the ECS claimed by Gabon has extended to the maritime areas within 200 nautical miles of the Republic of Congo, and there is a possibility of overlapping maritime areas. This suggests that the Republic of Congo does not object to the view that the other state’s ECS may not extend to an area within its 200 nautical miles.

B. The State Practice is not Sufficiently Representative

In addition to being sufficiently widespread, the practice in question must be sufficiently representative. Particular consideration should be given to the practices of states whose interests are specially affected.Footnote 60 The term “specially affected States” is defined as those “which are particularly involved in the relevant activity or are most likely to be concerned with the alleged rule”.Footnote 61 In its commentary on Conclusion 8 of the Draft Conclusions, the ILC emphasized the significance of considering the role of states “that had an opportunity or possibility of applying the alleged rule”. It is thus imperative to consider the circumstances of all states that have the opportunity or possibility of invoking the alleged rule.Footnote 62 In the context of Nicaragua v. Colombia, the specially affected states are those that can claim a continental shelf extending into 200 nautical miles from the baselines of another state, as well as those that are able to respond to such claims. Indeed, the parties to the present case have engaged in a debate on the representativeness of the relevant state practice. Colombia drew attention to the practices of a number of states in the Asia-Pacific region, Europe, Africa, and Latin America. Nicaragua, however, challenged the representativeness of these practices.Footnote 63 The Court has only made a passing reference to the practice of the non-parties to the UNCLOS.

The Court’s approach in the present case also departs from its established practice. To illustrate, in Fisheries Jurisdiction, the Court referred to an arrangement concerning fishing rights that had been concluded between states in the waters off the Faroe Islands to assess whether the preferential fishing rights of the coastal state had developed into a CIL. In particular, the Court observed that this arrangement included a number of interested states, including Belgium, Denmark, France, the Federal Republic of Germany, Norway, Poland, and the United Kingdom. Additionally, the Court made specific reference to an agreement concerning regulation of the fishing of north-east Arctic cod. This agreement was signed by certain major maritime states, including the United Kingdom, Norway, and the Soviet Union.Footnote 64 Similarly, in State Immunity, the Court provided a comprehensive and detailed examination of the domestic legislative practices in respect of state immunity of various countries, including the United States, the United Kingdom, South Africa, Canada, Australia, Singapore, Argentina, Israel, Japan, and Pakistan. Additionally, the Court examined the domestic judicial practices of France, Slovenia, Poland, Greece, and other countries with regard to the actions of the German armed forces during World War II, which were closely linked to the customary rule at issue in the case.Footnote 65 In Tunisia v. Libya, despite the fact that the exclusive economic zone regime had already been claimed by a significant number of states at that time, the Court, in its judgment, only prudently suggested that the exclusive economic zone regime “may be regarded as part of modern international law”.Footnote 66

In Nicaragua v. Colombia, there is a considerable amount of contradictory state practices, including those of China, Nicaragua, the Republic of Korea, Somalia, France, and Congo. To illustrate, a comparison can be made between the “Map of the Argentine continental shelf outer limit fixed points (RA) in the combined continental margin – North Scotia ridge” in Argentina’s 2009 submission to the CLCS and the “Map showing the outer limits of the Western Continental Shelf of the Chilean Antarctic Territory” in Chile’s 2022 submission to the CLCS. It can be observed that the “Map showing the outer limits of the Western Continental Shelf of the Chilean Antarctic Territory” illustrates that the limits of Chile’s EEZ and the 200-nautical-mile limit of the continental shelf in the maritime area surrounding the Diego Ramírez Islands do not align.Footnote 67 Additionally, the 200-nautical-mile limit of the continental shelf claimed by Argentina does not align with the 200-nautical-mile limit of Chile’s continental shelf in the Diego Ramírez Islands region. There is a degree of overlap between the continental shelf claimed by Argentina and the area of Chile’s continental shelf within 200 nautical miles.

In any event, given the considerable quantity and geographical distribution of the practice of the opposing states, all of which are coastal states whose rights are particularly affected by the CIL in question, the court’s conclusion that the practice of the vast majority of the contracting parties to the UNCLOS satisfies the requirement of identifying CIL is not persuasive.

C. The State Practice is not Sufficiently Consistent

The criterion of consistency plays an essential role in the evaluation of state practice and the identification of a general practice. In order to assess the uniformity of practice, it is necessary to consider all documented practices of a specific state in relation to the CIL in question.Footnote 68 In this regard, any contradictory or inconsistent practice must be taken into account in order to gain a comprehensive understanding of the subject matter.Footnote 69 It’s been suggested that both internal and collective consistency should be maintained so that a state and different states must not have engaged in substantially different practice.Footnote 70

In Nicaragua v. Colombia, the Court did not conduct an objective assessment of the totality of the submissions made by the relevant states to the CLCS. Furthermore, it did not assess the consistency of the relevant practices. Article 76(10) explicitly states that the provisions of this article are without prejudice to the question of delimitation of the continental shelf.Footnote 71 The objective of this paragraph is to guarantee that a coastal state’s claim to continental shelf in accordance with Article 76 of the Convention does not result in any prejudice or encroachment on the relevant rights of neighbouring states.Footnote 72 It can thus be argued that the self-constraint policies of those states in their submissions to the CLCS in accordance with Article 76(8) of the Convention provide substantial evidence in support of the Court’s conclusions. However, it is important to note that the submissions to the CLCS made by the contracting Parties to the UNCLOS in accordance with Article 76(8) are not definitive. Furthermore, state practice may manifest in other forms, and thus the submissions may not be reliable evidence for the purpose of determining the consistency of state practice.

It is possible that states have initially made partial submissions and subsequently revised the submissions. For example, the submission made by Somalia to the CLCS in 2014 referred to “for the purpose of this submission, the northernmost fixed point of the outer limit of the Somali continental shelf is established on the Yemeni 200 nautical miles line”.Footnote 73 This would indicate that the act of Somalia is consistent with the Court’s conclusion. However, in its revised submission in 2015, Somalia asserted that the “for the purpose of this Amendment, the northernmost fixed point of the outer limits of the Somalia continental shelf is established on the intersection of the Omani 200 nautical mile line”.Footnote 74 The schematic diagram of the amended submission made by Somalia in 2015 indicates that its claim to the continental shelf extends into 200 nautical miles from the baselines of Yemen.

Furthermore, the submissions made by France in 2007 with respect to the areas of French Guiana and French New Caledonia, in 2012 jointly with Tuvalu and New Zealand, and in 2018 in respect of the area of French Polynesia, have all stopped at 200 nautical miles from the baselines of another state.Footnote 75 However, a comparison of the schematic “Detailed map of the outer limit of the continental shelf in the area of the French Antilles” in the submission made by France in 2009 in respect of the area of the French Antilles and the Kerguelen Islands with the schematic “Map showing the final outer limits of the continental shelf of Barbados” in the submission made by Barbados in 2008 reveals that there is an overlap between the continental shelf beyond 200 nautical miles claimed by France and the continental shelf of Barbados within 200 nautical miles.Footnote 76 France claims an extension of its outer continental shelf into 200 nautical miles from the baselines of another state. This demonstrates that France’s approach does not align with the consistency required that is typically observed in similar cases.

On the other hand, a state’s submission to the CLCS may not be entirely consistent with its practice in other contexts. To illustrate, the submission made by the Maldives to the CLCS in 2010 restricts the extension of the continental shelf to 200 nautical miles from the baselines of Sri Lanka and India.Footnote 77 Nevertheless, in Maldives v. Mauritius, the Maldives advanced the argument that its ECS could extend to 200 nautical miles from the baselines of Mauritius.Footnote 78

Conclusion 7 of the Draft Conclusions states that the weight to be given to a practice may be reduced where the practice of a particular state varies.Footnote 79 It is evident that there is considerable variation in the positions of the states. In this regard, according to the ILC, the existence of a general practice cannot be substantiated when there are significant variations in the practice in question and it is challenging to discern a consistent pattern of conduct.Footnote 80 In Right of Asylum, the Court determined that there were an excessive number of uncertainties, contradictions, and variations in the practice of exercising the right of diplomatic asylum and in the positions of states with respect to the asylum-related conventions. Consequently, the Court was unable to conclude that there was a CIL existing with respect to the right of diplomatic asylum.Footnote 81 In Fisheries, the Court observed that while some states had incorporated the ten-nautical-mile rule into their national legislation and a number of bilateral and multilateral treaties and conventions, and while a number of arbitral awards between states had applied this rule, it was noted that other states had adopted different distances. In conclusion, the Court determined that the ten-nautical-mile rule for the line of the Gulf seal did not constitute a CIL.Footnote 82 In the present case, as Judge Tomka observed, the contrary practice of twenty states appears to be capable of calling into question the existence of a general practice.Footnote 83

III. Deficiencies in the ICJ’s Identification of Opinio Juris

In paragraph 77 of the Nicaragua v. Colombia judgment, the Court acknowledged that the practice of states in making submissions to the CLCS may be partly motivated by considerations other than a sense of legal obligation. Nevertheless, the Court still considered the state practice evidenced opinio juris. The subsequent section will demonstrate that the actions of the states in question should not be regarded as indicative of opinio juris, given that their motivation is not primarily rooted in a sense of legal obligation.

A. The Criteria for Identifying Opinio Juris

Opinio juris is a subjective component of CIL. It implies that the general practice in question must be accompanied by a “conviction that such practice is permitted, required, or prohibited by customary international law”.Footnote 84 This conviction is a distinctive feature of opinio juris, which sets it apart from other motives for behaviours that are not legally binding, such as comity, reciprocity, political expediency, convenience, tradition, and so forth.Footnote 85 Evidence of opinio juris manifests in various forms, and the conduct of the states involved should be subjected to careful analysis to ascertain whether it accurately reflects a state’s view of the CIL.Footnote 86 In addition, while the two elements of CIL may coexist within the same evidentiary material, it is essential to identify each element separately.Footnote 87

The opinio juris is of pivotal importance in the formation and maintenance of a CIL. It is evident that the mere conduct of states cannot be equated with law. Rather, such practice can only become law if states intentionally facilitate a transformation into law.Footnote 88 Furthermore, the ILC’s commentary to conclusion 3 of the Draft Conclusions notes that in the context of prohibitive rules, it can be difficult to identify significant affirmative state practice (as opposed to inaction). In such cases, the evaluation of inaction may be a key factor in determining whether it is accepted as law.Footnote 89 The motives behind state action are often unclear. As a result, the evaluation of opinio juris represents a crucial method for determining whether the conduct in question is based on a perception of legal obligation.Footnote 90

B. The Evidence Relied Upon by the ICJ to Establish Opinio Juris

In their dissenting opinions, Judges Skotnikov and Robinson advanced a critical perspective on the Court’s determination of opinio juris in light of the CLCS submissions. The Court’s assumption of the existence of opinio juris based on the self-constraint policies of 39 states was deemed implausible, given that such practice could be driven by factors other than a sense of legal obligation.Footnote 91 Furthermore, Judge Skotnikov drew attention to The Military and Paramilitary Activities, in which it was stated that the Court did not have “authority to ascribe to States legal views which they do not themselves advance”.Footnote 92 Indeed, in Lotus, the Permanent Court of International Justice had already expressed concern about the separation between general practice and opinio juris. France had advanced the argument that prosecutions in cases of collisions of ships on the high seas were conducted exclusively within the jurisdiction of the flag state. This stance reflected the assumption that other states had implicitly consented to this arrangement. The Permanent Court did not endorse France’s assertion, instead, it held that these circumstances merely demonstrated that states often waived the institution of criminal proceedings in practice. This did not imply that they considered themselves bound to do so. An international custom can only be involved if such a waiver was based on an awareness of the existence of an obligation.Footnote 93

Similarly, in the present case, it is not possible to ascertain the motives behind the behaviour of the states in the CLCS submissions based on the publicly available preliminary information or the Executive Summary of the submissions alone. Furthermore, the objections raised by those states that have opposed the claims of an ECS within 200 nautical miles from the baselines of another state do not directly corroborate the Court’s conclusions. For example, Japan has indicated its opposition to specific aspects of the submissions made by China and the Republic of Korea. Japan advanced the argument that the CLCS should refrain from considering the submissions on the grounds that the distances between the coasts of Japan and China/Korea were less than 400 nautical miles. The states concerned shall delimitate the continental shelves in accordance with Article 83 of the UNCLOS.Footnote 94 In this instance, Japan has not explicitly stated that its claim is based on the CIL as identified by the Court. In its reply to Japan’s note verbale, Korea has stated that the two legal bases for continental shelf rights established by the UNCLOS, namely the distance criterion and the geomorphological criterion, are not mutually exclusive. Japan cannot negate Korea’s continental shelf right based on the geomorphological criterion by its right based on the distance criterion.Footnote 95 As Holly Leung has observed, these objections are the reactions of states to the assertion of an ECS by other states, rather than the assertion of an ECS by a former state that complies with the alleged customary rule. The latter would constitute supportive state practice. However, it is unclear how the objecting state’s reaction alone can demonstrate its compliance with an alleged customary rule on the extent of the ECS, given that it has not even asserted an ECS.Footnote 96

In conclusion, while it cannot be definitively excluded that some of the practice may substantiate the Court’s assertion of opinio juris, it is also evident that other factors have driven the states to adopt a self-constraint policy in their submissions to the CLCS.

First, a state may have exercised restraint to ensure that the submission in question might be considered by the CLCS. In accordance with Rule 46 and Paragraph 5(a) of Annex I to the CLCS Rules of Procedure, the Commission shall not proceed with the consideration of a submission made in the context of a dispute between states with opposite or adjacent coasts or other unresolved land or maritime disputes, unless the parties to the dispute so agree.Footnote 97 This stipulation may prevent the CLCS from considering certain submissions.Footnote 98 As a result, a state may refrain from asserting an ECS that extends within 200 nautical miles from the baselines of another state.Footnote 99 To illustrate, in Barbados and Trinidad and Tobago, Trinidad and Tobago explicitly asserted a continental shelf that extended within 200 nautical miles from the baselines of Barbados.Footnote 100 However, in its submission to the CLCS in 2009, that state adopted a policy of self-constraint. In the Executive Summary, Trinidad and Tobago stated that, in view of the fact that it had not been possible to obtain from Barbados a commitment similar to that given by other neighbouring states not to object to the CLCS’s consideration of its submission, the submission “is not dependent on the utilization of maritime space within 200 Ms of the Barbados coastline”.Footnote 101 It is evident that Trinidad and Tobago was driven by the objective of achieving an “absence of dispute” at the time of its submission.

Second, it is possible that a state has exercised self-constraint in order to fulfil its obligations as set out in the relevant delimitation treaties. In this regard, the ILC has stated that where a state’s compliance with an obligation is motivated by a treaty, such practice cannot be regarded as opinio juris for the purpose of identifying CIL.Footnote 102 In this context, Judge Xue Hanqin, in her separate opinion in Nicaragua v. Colombia, highlighted that approximately one-third of the states that had adopted the self-constraint policy had concluded bilateral agreements with their neighbours on the delimitation of the continental shelf within 200 nautical miles of the baselines.Footnote 103 For instance, a comparison of Russia’s continental shelf submission to the CLCS in 2001, namely the schematic “Area of the continental shelf of the Russian Federation in the Arctic Ocean beyond 200-nautical-mile zone”, with the schematic “The continental shelf beyond 200 nautical miles in the Loop Hole in the Barents Sea” in Norway’s submission of 2006, reveals that a portion of Russia’s claimed continental shelf beyond 200 nautical miles extends within 200 nautical miles of Norway’s claim.Footnote 104 In 2010, Russia and Norway concluded the Treaty on Maritime Delimitation and Cooperation in the Barents Sea and the Arctic Ocean. This treaty establishes the limits of the easternmost part of the outer limit of the Norwegian continental shelf and the westernmost part of the outer limit of the Russian continental shelf. Under these circumstances, the revised submission made by Russia in 2015 removed the portion of the extension within 200 nautical miles from the baselines of Norway.Footnote 105

In addition, in its submission to the CLCS in 2009, Palau exhibited a tendency to constrain the extent of its ECS. In this context, Palau explicitly acknowledged the impact of the outstanding delimitation issues with the adjacent or opposite coastal states in its submission.Footnote 106 In 2006, Palau and the Micronesian State concluded the Treaty on Maritime Boundaries and Co-operation in Respect of Related Matters, which delimitated the boundary of the EEZ. Article 2(3) of that Treaty explicitly states that it is without prejudice to the claims of the parties to extend their continental shelves, provided that neither party shall claim an ECS into the exclusive economic zone of the other party.Footnote 107 In the light of the foregoing, it is reasonable to conclude that if Palau considered that there was a CIL as identified by the Court, it is redundant for the Treaty to include such a provision. Thus, it can be concluded that Palau’s self-constraint approach is driven by a commitment to the principle of pacta sunt servanda.

Third, states may adopt the self-constraint policy in order to achieve an equitable solution to maritime delimitation disputes. Judge Charlesworth, in her dissenting opinion, articulated the rationale behind this perspective on the motives of states.Footnote 108 Articles 74 and 83 of the UNLCLOS establish the principle of an equitable solution of disputes concerning the delimitation of the EEZ and continental shelf. The Court has developed a “three-stage methodology” to ensure predictability in the delimitation process.Footnote 109 According to this method of delimitation, wherein the distance between two coastal states exceeds 400 nautical miles, the establishment of a provisional equidistance line or median line based on the appropriate points on the coasts of the two states will inevitably result in both parties possessing a continental shelf of at least 200 nautical miles. A situation may arise in which one or more coastal states have an entitlement to a continental shelf beyond 200 NM, but in which they are located in such a way that the equidistance line – or median line in the case of opposite coasts – constructed from the coast lies beyond the area of overlapping entitlements.Footnote 110 However, this may constitute a relevant circumstance that would provide grounds for that state to claim an adjustment to the provisional equidistance line.Footnote 111 In this context, the exercise of self-constraint may be a pragmatic means of avoiding diplomatic and legal disputes as any other course of action.

Fourth, a state’s self-constraint policy may be driven by reciprocity or political considerations. The Court has previously acknowledged the existence of such non-legal considerations. In the Right of Passage, the Court held that Portugal’s armed forces and police, among others, were not entitled to free passage under customary international law. This was due to fact that the passage of the armed forces and police between the British and Portuguese possessions during the period of British rule prior to 1878 was subject to the principles of reciprocity and could not therefore be regarded as a right of free passage.Footnote 112

Similarly, in Mauritius v. Maldives, the Maldives asserted that its continental shelf could extend within 200 nautical miles from the baselines of Mauritius.Footnote 113 Mauritius raised an objection, which was not based on the existence of a customary rule. Rather, it was based on the relevant commitments made by the Maldives during the negotiations on the maritime boundary between the two states in 2010.Footnote 114 Moreover, Mauritius has advanced the argument that if the Maldives is entitled to claim an outer continental shelf within 200 nautical miles from the baselines of Mauritius, then Mauritius is similarly entitled to claim an extension of its outer continental shelf within 200 nautical miles from the baselines of the Maldives.Footnote 115 It is evident that Mauritius’s self-constraint with regard to the ECS is based on a consideration of reciprocity. In his separate opinion, Judge Iwasawa, stated that

States usually do not curtail themselves when they believe that they have a right. If an issue is regulated by international law and States abstain from certain conduct in a way that is inconsistent with their own interests, it may be presumed that their abstention is motivated by a sense of legal obligation.Footnote 116

It is evident that Mauritius’s self-constraint policy contradicts this presumption.

In conclusion, the motivations for states’ self-constraint actions in the CLCS submissions are diverse. These include the avoidance of the CLCS’s non-consideration of the submission, compliance with obligations under existing treaties, reciprocity, and other non-legal considerations.Footnote 117 This is precisely what Judge Robinson has emphasized in his dissenting opinion, that the Court’s presumption of opinio juris in Nicaragua v. Colombia could be rebutted by the very clear possibility that the practice of self-constraint may be explained by considerations other than a sense of legal obligation.Footnote 118 In contrast to the Court’s cautious approach to identifying opinio juris in cases such as the North Sea Continental Shelf and the Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons,Footnote 119 the Court in the present case did not rely on conclusive evidence to establish the existence of opinio juris. Instead, the Court derived opinio juris from certain state practice, which does not reflect a sense of legal obligation.

It is noteworthy that, in paragraph 77 of its judgment, the Court, when quoting from Gulf of Maine, omitted the second half of the sentence originally included in the judgment:

A body of detailed rules is not to be looked for in customary international law which in fact comprises a limited set of norms for ensuring the co-existence and vital co-operation of the members of the international community, together with a set of customary rules whose presence in the opinion juris of States can be tested by induction based on the analysis of a sufficiently extensive and convincing practice, and not by deduction from preconceived ideas.Footnote 120

IV. Conclusions

In Nicaragua v. Colombia, the ICJ ruled that, in accordance with CIL, a state’s entitlement to a continental shelf beyond 200 nautical miles from the baselines from which the breadth of its territorial sea is measured may not extend within 200 nautical miles from the baselines of another state. The two-element approach is regarded as the fundamental methodology for identifying CIL. By this approach, it is necessary to identify the two constituent elements of CIL, namely general practice and opinio juris, independently. In identifying this customary rule, the Court did not adhere to the two-element approach. In identifying the general practice, the Court relied primarily on the submissions made by 39 states to the CLCS and the practice of certain non-Parties to the UNCLOS. The Court failed to consider the contradictory and inconsistent conducts of numerous states, particularly those of the specially affected states. The state practice relied upon by the Court fails to meet the requisite criteria for identifying a general practice, namely that it must be sufficiently widespread, representative, and consistent. The Court inferred the existence of opinio juris from the state practice in question, which did not necessarily reflect a sense of legal obligation.

The Court has established a customary rule with the following legal implications. First, it can be deduced from the Court’s decision that the legal basis of a coastal state’s entitlement to the continental shelf differs depending on whether the area in question is situated within or beyond 200 nautical miles from its baselines. In the area within 200 nautical miles, the legal basis is distance; beyond this limit, it is natural prolongation. Second, within the 200-nautical-mile limit, the criterion of distance is considered to have precedence over that of natural prolongation in the event of a conflict.Footnote 121 Third, the Court’s decision appears to imply that only the continental shelf rights within 200 nautical miles are truly inherent rights, which directly challenges the notion of a single continental shelf in the law of the sea.Footnote 122 Lastly, the Court’s decision would introduce a third line of limitation to the two lines of limitation set forth in Article 76(5) of the Convention, namely the extent of another state’s 200 nautical miles limit. As observed by Hilde Woker, in contrast to the two limitation lines under Article 76(5), whereby the coastal states may select the more favourable of the two lines, this third limitation leaves no room for choice and is more prominent than the two original limitation lines.Footnote 123 The Court’s decision can be regarded as a rewriting of the provisions of the UNCLOS, thereby constituting an act of law-making. This process has taken place without the involvement of the contracting Parties to the Convention, yet it may have a significant impact on the establishment of the outer limits of the continental shelf, the delimitation of maritime boundaries, and the resolution of maritime disputes. It is imperative to maintain a rigorous and ongoing monitoring and analysis of the implications of the Court’s ruling in the Nicaragua v. Colombia case.

Acknowledgements

The authors would like to thank the reviewers for their invaluable comments.

Funding statement

The authors benefited from a key research project (number 22VHQ004) of the National Social Sciences Fund of China in writing this article.

Competing interests

The authors declare none.

References

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2 Nicaragua v. Colombia Case, supra note 1 at 34, para. 104.

3 Hilde WOKER, “Preliminary Reflections on the ICJ Judgment in Question of the Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Nicaraguan Coast (Nicaragua v. Colombia) of 13 July 2023” (21 July 2023), online: EJIL:Talk! www.ejiltalk.org/preliminary-reflections-on-the-icj-judgment-in-question-of-the-delimitation-of-the-continental-shelf-between-nicaragua-and-colombia-beyond-200-nautical-miles-from-the-nicaraguan-coast-nicaragua-v-co/; All websites accessed on 15 August 2024, unless otherwise mentioned.

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5 Territorial and Maritime Dispute Case, supra note 4 at 719, para. 251.

6 Commission on the Limits of the Continental Shelf, “Submission of the Republic of Nicaragua to the Commission on the Limits of the Continental Shelf” (1 July 2013), online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/nic66_13/clcs66_2013.pdf.

7 Nicaragua v. Colombia Case, supra note 1 at 15, paras. 25–6.

8 Ibid., at 8, para. 10.

9 Ibid., at 8, para. 14.

10 Ibid., at 29, para. 77.

11 Nicaragua v. Colombia Case, supra note 1, Separate Opinion of Judge Xue; Dissenting Opinion of Judge Tomka; Dissenting Opinion of Judge Robinson; Dissenting Opinion of Judge Charlesworth; Dissenting Opinion of Judge Ad Hoc Skotnikov.

12 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Tomka, at 2–3, paras. 4–8.

13 Yoshifumi TANAKA, “Recent Developments in the Jurisprudence Concerning the Delimitation of the Continental Shelf Beyond 200 Nautical Miles: Analysis of the Mauritius/Maldives and Nicaragua v. Colombia Cases” (2024) 103 International Law Studies 74; Xinjun ZHANG and Xidi CHEN, “The 2022 ICJ Judgment in Nicaragua v. Colombia: Towards a Theory of Exclusivity in Allocating Rights and Jurisdiction between the Coastal and Other States?” (2024) 23 (2) Chinese Journal of International Law 223; Christopher WARD, “Question of the Delimitation of the Continental Shelf Between Nicaragua and Colombia Beyond 200 Nautical Miles from the Nicaraguan Coast (Nicar. v. Colom.)” (2024) 118 (2) American Journal of International Law 324; Matei ALEXIANU, “The Nicaragua v. Colombia Continental Shelf Judgment: Short But Significant” (29 September 2023), online: ASIL Insights https://www.asil.org/insights/volume/27/issue/9; Holly LEUNG, “The Extended Continental Shelf in Nicaragua v Colombia: Identifying a Customary Rule Based on CLCS Submissions?” (2024) 55 (1-2) Ocean Development & International Law 206 at 207–8.

14 Vito DE LUCIA, “On the Question of opinio juris in Nicaragua vs. Colombia (Judgement 13 July 2023)” (3 August 2023), online: EJIL:Talk! www.ejiltalk.org/on-the-question-of-opinio-juris-in-nicaragua-vs-colombia-judgement-13-july-2023/; Hilde Woker, supra note 3; Keshav SOMANI, “The ICJ’s Judgment in Nicaragua v. Colombia: Back to the Basics” (16 August 2023), online: Opinio Juris https://opiniojuris.org/2023/08/16/the-icjs-judgment-in-nicaragua-v-colombia-back-to-the-basics/.

15 Nicaragua v. Colombia Case, supra note 1 at 28–9, para. 76.

16 Ibid.

17 Delimitation of the maritime boundary in the Bay of Bengal (Bangladesh/Myanmar), Judgment of 14 March 2012, ITLOS, Rep. 4 at 120–1, paras. 471–6 (hereinafter, Bay of Bengal Case); Maritime Delimitation in the Indian Ocean (Somalia v. Kenya), Judgment of 12 October 2021, I.C.J. Rep. 206 at 270–7, paras. 178–97 (hereinafter, Somalia v. Kenya Case); Dispute concerning delimitation of the maritime boundary between Mauritius and Maldives in the Indian Ocean (Mauritius v. Maldives), Judgment of 28 April 2023, ITLOS, Case No.28 at 97–102, paras. 257–75 (hereinafter, Mauritius v. Maldives Case).

18 Statute of the International Court of Justice (entered into force 24 October 1945), art. 59.

19 Malcolm D. EVANS and Nicholas A. IOANNIDES, “A Commentary on the 2023 Nicaragua v. Colombia Case” (4 August 2023), online: EJIL:Talk! www.ejiltalk.org/a-commentary-on-the-2023-nicaragua-v-colombia-case/; Xuexia LIAO, “Is There a Hierarchical Relationship between Natural Prolongation and Distance in the Continental Shelf Delimitation?” (2018) 33 The International Journal of Marine and Coastal Law 79 at 83.

20 Hugh THIRLWAY, The Sources of International Law, 2nd ed. (Oxford: Oxford University Press, 2019) at 64.

21 Michael WOOD and Omri SENDER, Identification of Customary International Law (Oxford: Oxford University Press, 2024) at 3.

22 Nicaragua v. Colombia Case, supra note 1 at 22, para. 46; Continental Shelf (Libyan Arab Jamahiriya v. Malta), Judgment of 3 June 1985, I.C.J. Rep. 13 at 29–30, para. 27 (hereinafter, Libya v. Malta Case).

23 Fernando Lusa BORDIN, “A Glass Half Full? The Character, Function and Value of the Two-Element Approach to Identifying Customary International Law” (2019) 21 (3–4) International Community Law Review 283 at 285; Omri SENDER and Michael WOOD, “A Mystery No Longer? Opinio Juris and Other Theoretical Controversies Associated with Customary International Law” (2017) 50 (3) Israel Law Review 299 at 305–6.

24 Statute of the International Court of Justice, supra note 18, art. 38(1)(b).

25 Birgit SCHLUTTER, Developments in Customary International Law: Theory and the Practice of the International Court of Justice and the International ad hoc Criminal Tribunals for Rwanda and Yugoslavia (Leiden/Boston: Martinus Nijhoff Publishers, 2010) at 13.

26 International Law Commission, “International Law Commission, Draft Conclusions on Identification of Customary International Law, With Commentaries” (hereinafter, ILC Draft Conclusions), UN Doc. A/73/10 (2018), at 124, online: ILC https://legal.un.org/ilc/texts/instruments/english/commentaries/1_13_2018.pdf.

27 Ibid., at 126.

28 Omri SENDER and Michael WOOD, “Custom’s Bright Future: The Continuing Importance of Customary International Law” in C. BRADLEY, Custom’s Future: International Law in a Changing World (Cambridge: Cambridge University Press, 2016) at 365–6; Bordin, supra note 23 at 285.

29 Karol WOLFKE, Custom in Present International Law, 2nd ed. (Leiden/Boston: Martinus Nijhoff Publishers, 1993) at 40–1; Sender and Wood, supra note 23 at 305–6.

30 Bordin, supra note 23 at 290–1; Thirlway, supra note 20 at 71.

31 ILC Draft Conclusions, supra note 26 at 125.

32 Nicaragua v. Colombia Case, supra note 1 at 27–8, paras. 70–6.

33 Nicaragua v. Colombia Case, supra note 1, Public Sitting, [2022] CR 2022/27, at 16–21; Nicaragua v. Colombia Case, supra note 1, Public Sitting, [2022] CR 2022/28, at 18–23.

34 Nicaragua v. Colombia Case, supra note 1 at 29, para. 77.

35 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Tomka, at 17, para. 58.

36 ILC Draft Conclusions, supra note 26 at 127.

37 Ibid., at 128–9.

38 Nicaragua v. Colombia Case, supra note 1 at 29, para. 77.

39 Ibid., at 24, 26, paras. 57, 67.

40 Jurisdictional Immunities of the State (Germany v. Italy: Greece intervening), Judgment of 3 February 2012, I.C.J. Rep. 99 at 122–3, 128–35, paras. 55, 66–78 (hereinafter, State Immunity Case).

41 Thirlway, supra note 20 at 74; Michael WOOD, “The Present Position within the ILC on the Topic ‘Identification of Customary International Law’: in Partial Response to Sienho YEE, ‘Report on the ILC Project on ‘Identification of Customary International Law’’” (2016) 15 Chinese Journal of International Law 3 at 8.

42 ILC Draft Conclusions, supra note 26 at 130.

43 Ibid., at 133.

44 Maurice H. MENDELSON, “The Formation of Customary International Law” (1998) 272 Recueil des cours de l’Académie de La Haye en ligne 155 at 197.

45 ILC Draft Conclusions, supra note 26 at 134–5.

46 Jörg KAMMERHOFER, “Uncertainty in the Formal Sources of International Law: Customary International Law and Some of Its Problems” (2004) 15 (3) European Journal of International Law 523 at 530–1; Sender and Wood, supra note 21 at 308.

47 ILC Draft Conclusions, supra note 26 at 136.

48 Ibid., at 126.

49 Katie A. JOHNSTON, “The Nature and Context of Rules and the Identification of Customary International Law” (2021) 32 (4) European Journal of International Law 1167 at 1172–4.

50 North Sea Continental Shelf (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands), Judgment of 20 February 1969, I.C.J. Rep. 3 at 51, para. 96 (hereinafter, North Sea Continental Shelf Case); Continental Shelf (Tunisia v. Libyan Arab Jamahiriya), Judgment of 24 February 1982, I.C.J. Rep. 18 at 61, para. 73 (hereinafter, Tunisia v. Libyan Arab Jamahiriya Case); Maritime Delimitation in the Black Sea (Romania v. Ukraine), Judgment of 3 February 2009, I.C.J. Rep. 61 at 89, para. 77 (hereinafter, Black Sea Case).

51 Convention on the Continental Shelf, 29 April 1958, 499 U.N.T.S 311 (entered into force 10 June 1964), art. 2(3); United Nations Convention on the Law of the Sea, 10 December 1982, 1833 U.N.T.S. 396 (entered into force on 16 November 1994) [UNCLOS], art. 77(3).

52 Evans and Ioannides, supra note 19; Hilde WOKER, “Challenging the Notion of a ‘Single Continental Shelf’” (2023) 54 (4) Ocean Development & International Law 375 at 381–2; Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Robinson, at 1, para. 2; Ward, supra note 13 at 330–1; Alexianu, supra note 13 at 5–6.

53 Panos MERKOURIS, Jörg KAMMERHOFER and Noora ARAJÄRVI, eds., The Theory, Practice, and Interpretation of Customary International Law (Cambridge: Cambridge University Press, 2022) at 337–40.

54 North Sea Continental Shelf, supra note 50, Separate Opinion of Judge Fouad Ammoun, at 130

55 Fisheries Jurisdiction (United Kingdom v. Iceland), Judgment of 25 July 1974, I.C.J. Rep. 3 at 26, para. 58 (hereinafter, Fisheries Jurisdiction Case).

56 Nicaragua v. Colombia Case, supra note 1, Separate Opinion of Judge Xue, at 16, para. 38; Nicaragua v. Colombia Case, supra note 1, Public Sitting, [2022], CR 2022/27, at 20, para. 13.

57 Commission on the Limits of the Continental Shelf, “Partial Submission to the Commission on the Limits of the Continental Shelf, pursuant to Article 76, paragraph 8 of the United Nations on the Law of the Sea in respect of the Area of Saint-Pierre-et-Miquelon” (16 April 2014), at 5, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/fra72_14/SPM_Summary_EN_April2014.pdf; Commission on the Limits of the Continental Shelf, “Partial Submission of Canada to the Commission on the Limits of the Continental Shelf regarding its Continental Shelf in the Atlantic Ocean” (6 December 2013), at 13, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/can70_13/es_can_en.pdf.

58 Commission on the Limits of the Continental Shelf, “Submission made by the Gabonese Republic for the Extension of its Continental Shelf beyond 200 Nautical Miles pursuant to Article 76 of the United Nations on the Law of the Sea” (10 April 2012), online: CLCS www.un.org/depts/los/clcs_new/submissions_files/gab60_12/Executive_Summary_eng. pdf.

59 Commission on the Limits of the Continental Shelf, “Communications received with regard to the submission made by Gabon to the Commission on the Limits of the Continental Shelf”, Republic of the Congo, 13 July 2021, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/gab60_12/20210713CogNvUn001E.pdf.

60 Mendelson, supra note 44 at 219.

61 ILC Draft Conclusions, supra note 26 at 136.

62 Ibid., at 136–7.

63 Nicaragua v. Colombia Case, supra note 1, Public Sitting, 7 December 2022, CR 2022/27, at 16–20, paras. 7–12; Nicaragua v. Colombia Case, supra note 1, Public Sitting, 6 December 2022, CR 2022/26, at 35–42, paras. 12–47.

64 Fisheries Jurisdiction Case, supra note 55 at 26, para. 58.

65 State Immunity Case, supra note 40 at 130–4, paras. 70–6.

66 Tunisia v. Libyan Arab Jamahiriya Case, supra note 50 at 74, para. 100.

67 Commission on the Limits of the Continental Shelf, “Outer Limit of the Continental Shelf Argentine Submission” (21 April 2009), at 21, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/arg25_09/arg2009e_summary_eng.pdf; Commission on the Limits of the Continental Shelf, “Partial Submission of Chile to the Commission on the Limits of the Continental Shelf” (28 February 2022), at 14, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/chl_89_2022/2022-CHL-WCAT-ES-eng_secured.pdf.

68 ILC Draft Conclusions, supra note 26 at 134–5.

69 Ibid., at 135–6.

70 Mendelson, supra note 44 at 212.

71 UNCLOS, art. 76(10).

72 Alex ELFERINK and Constance JOHNSON, “Outer Limits of the Continental Shelf and Disputed Areas: State Practice Concerning Article 76(10) of the LOS Convention” (2006) 21 (4) The International Journal of Marine and Coastal Law 461 at 463–4.

73 Commission on the Limits of the Continental Shelf, “Continental Shelf Submission of the Federal Republic of Somalia Executive Summary” (21 July 2014), at 11, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/som74_14/Somalia_Executive_Summary_2014.pdf.

74 Commission on the Limits of the Continental Shelf, “Continental Shelf Submission of the Federal Republic of Somalia Executive Summary Amended” (16 July 2015), at 8–9, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/som74_14/2015-07-16_SOM-DOC-001.pdf.

75 Commission on the Limits of the Continental Shelf, “Partial Submission to the Commission on the Limits of the Continental Shelf, pursuant to Article 76, paragraph 8 of the United Nations on the Law of the Sea in respect of the Area of French Guiana and New Caledonia” (22 May 2007), at 3, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/fra07/fra_executivesummary_2007.pdf; Commission on the Limits of the Continental Shelf, “Joint Submission to the Commission on the Limits of the Continental Shelf by Tuvalu, the Republic of France and New Zealand (Tokelau) Executive Summary” (7 December 2012), at 4, 7, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/tft62_12/tft_exsum_doc.pdf; Commission on the Limits of the Continental Shelf, “Partial Submission to the Commission on the Limits of the Continental Shelf, pursuant to Article 76, paragraph 8 of the United Nations on the Law of the Sea in respect of the area of French Polynesia” (6 April 2018), at 4, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/fra79_18/Part1_Summary_French_Polynesia_EN.pdf.

76 Commission on the Limits of the Continental Shelf, “Partial Submission to the Commission on the Limits of the Continental Shelf, pursuant to Article 76, paragraph 8 of the United Nations on the Law of the Sea in respect of the area of the French Antilles and the Kerguelen Islands” (5 February 2009), at 5, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/fra09/fra_executivesummary_2009.pdf; Commission on the Limits of the Continental Shelf, “Continental Shelf Submission of Government Barbados Executive Summary” (8 May 2008), at 3, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/brb08/brb08_executive_summary.pdf.

77 Commission on the Limits of the Continental Shelf, “Submission by the Republic of Maldives to the Commission on the Limits of the Continental Shelf Executive Summary” (26 July 2010), at 10, 16, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/mdv53_10/MAL-ES-DOC.pdf.

78 Mauritius v. Maldives Case, supra note 17 at 100, para. 267.

79 ILC Draft Conclusions, supra note 26 at 134.

80 Ibid., at 137.

81 Colombian-Peruvian Asylum Case, Judgment of 20 November 1950, I.C.J. Rep. 266 at 277.

82 Fisheries Case (United Kingdom v. Norway), Judgement of 18 December 1951, I.C.J. Rep. 116 at 131/

83 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Tomka, at 15, para. 49.

84 ILC Draft Conclusions, supra note 26 at 138.

85 Ibid.

86 Ibid., at 140.

87 Ibid., at 140–1.

88 Sienho YEE, “The News That Opinio Juris Is Not a Necessary Element of Customary [International] Law Is Greatly Exaggerated” (2000) 43 German Yearbook of International Law 227 at 237–8.

89 ILC Draft Conclusions, supra note 26 at 128.

90 Mendelson, supra note 44 at 271–3; Johnston, supra note 47 at 1175.

91 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Ad Hoc Skotnikov, at 3; Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Robinson, at 3, para. 9.

92 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Ad Hoc Skotnikov, at 3, para. 16.

93 Lotus, Judgment No. 9, [1927], P.C.I.J., Series A, No. 10, at 28.

94 Commission on the Limits of the Continental Shelf, “Communications with regard to the submission made by the Republic of Korea to the Commission on the Limits of the Continental Shelf”, Japan, 11 January 2013, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/kor65_12/jpn_re_kor_11_01_2013.pdf; Commission on the Limits of the Continental Shelf, “Communications with regard to the submission made by China to the Commission on the Limits of the Continental Shelf”, Japan, 28 December 2012, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/chn63_12/jpn_re_chn_28_12_2012.pdf.

95 Commission on the Limits of the Continental Shelf, “Communications with regard to the submission made by China to the Commission on the Limits of the Continental Shelf”, Republic of Korea, 23 January 2013, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/kor65_12/kor_re_jpn_23_01_2013.pdf.

96 Leung, supra note 13 at 214.

97 Rules of Procedure of the Commission on the Limits of the Continental Shelf, 17 April 2008, CLCS/40/Rev.1, rule 46, annex 1 5(a).

98 Signe Veierud BUSCH, Establishing Continental Shelf Limits beyond 200 Nautical Miles by the Coastal State: A Right of Involvement for Other States? (Leiden/Boston: Brill Nijhoff Publishers, 2016) at 99–102; 107–12; Oystein JENSEN, The Commission on the Limits of the Continental Shelf: Law and Legitimacy (Leiden/Boston: Brill Nijhoff Publishers, 2014) at 65–6.

99 Liao, supra note 19 at 95–6.

100 Arbitration between Barbados and the Republic of Trinidad and Tobago, Award of 11 April 2006, at 53–5, 109, paras. 174–8, 367.

101 Commission on the Limits of the Continental Shelf, “Submission to the Commission on the Limits of the Continental Shelf, pursuant to Article 76, paragraph 8 of the United Nations on the Law of the Sea, Republic of Trinidad and Tobago, Executive Summary” (12 May 2009), at 17–18, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/tto49_09/tto2009executive_summary.pdf.

102 ILC Draft Conclusions, supra note 26 at 139.

103 Nicaragua v. Colombia Case, supra note 1, Separate Opinion of Judge Xue, at 16, para. 40.

104 Commission on the Limits of the Continental Shelf, “Submission made by the Russian Federation to the Commission on the Limits of the Continental Shelf” (20 December 2001), online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/rus01/RUS_CLCS_01_2001_LOS_2.jpg; Commission on the Limits of the Continental Shelf, “Submission made by the Kingdom of Norway to the Commission on the Limits of the Continental Shelf, Executive Summary” (27 November 2006), at 13, online: CLCS www.un.org/depts/los/clcs_new/submissions_files/nor06/nor_exec_sum.pdf.

105 Commission on the Limits of the Continental Shelf, “Partial Revised Submission of the Russian Federation to the Commission on the Limits of the Continental Shelf, Executive Summary” (3 August 2015), at 22–3, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/rus01_rev15/2015_08_03_Exec_Summary_English.pdf.

106 Commission on the Limits of the Continental Shelf, “Submission to the Commission on the Limits of the Continental Shelf, pursuit to Article 76, paragraph 8 of the United Nations on the Law of the Sea, The Republic of Palau, Executive Summary” (8 May 2009), at 8, online: CLCS www.un.org/Depts/los/clcs_new/submissions_files/plw41_09/plw2009executivesummary.pdf.

107 Treaty between the Federated States of Micronesia and the Republic of Palau Concerning Maritime Boundaries and Cooperation on Related Matters (with annex and map), 16 July 2006, online: https://treaties.un.org/doc/Publication/UNTS/No%20Volume/54767/Part/I-54767-08000002804c7001.pdf. [FSM-PALAU].

108 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Charlesworth, at 11–12, paras. 31–4.

109 Somalia v. Kenya Case, supra note 17 at 248–51, paras. 119–25; Black Sea Case, supra note 49 at 101–3, paras. 115–22.

110 Woker, supra note 52 at 388–9.

111 Libya v. Malta Case, supra note 22 at 33, para. 33.

112 Case concerning Right of Passage over Indian Territory (Merits), Judgment of 12 April 1960, I.C.J. Rep. 6 at 38–9.

113 Mauritius v. Maldives Case, supra note 17 at 100, para. 267.

114 Ibid., at 98, para. 260.

115 Ibid., at 99, para. 264.

116 Nicaragua v. Colombia Case, supra note 1, Separate Opinion of Judge Iwasawa, at 3, para. 12.

117 Liao, supra note 19 at 103–4; Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Tomka, at 16, para. 53.

118 Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Robinson, at 4.

119 North Sea Continental Shelf Case, supra note 50 at 43–4, paras. 76–7; Legality of the Threat or Use of Nuclear Weapons Case, Advisory Opinion, [1996] I.C.J. Rep. 226 at 253–4, paras. 63–7.

120 Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada v. United States of America), Judgment of 12 October 1984, I.C.J. Rep. 246 at 299, para. 111; Nicaragua v. Colombia Case, supra note 1 at 29, para. 77.

121 Evans and Ioannides, supra note 19.

122 Woker, supra note 52 at 381–2.

123 Hilde WOKER, “A New Constraint to the Entitlement of a Continental Shelf beyond 200 Nautical Miles? Implications of the Recent Case Law” (2024) The International Journal of Marine and Costal Law 1 at 18; Nicaragua v. Colombia Case, supra note 1, Dissenting Opinion of Judge Robinson, at 1, para. 2.