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Published: Fri, 02 Feb 2018

North Sea Continental Shelf Cases

In his dissenting opinion in the North Sea Continental Shelf Cases Judge Tanaka described customary international law as “…Both delicate and difficult”. Discuss

Although the description of customary international law as being both delicate and difficult pertained specifically to the case before the International Court of Justice (“the ICJ”), the comment is not lost on the perplexity surrounding the origins and existence of customary international law itself. Whilst the existence of customary international law is now, to a greater extent, universally accepted in an abstract sense, it is exactly what determines it that has generated a great difference of opinions. Moreover, the very nature of customary international law has continually been called into question as regards its constitution in the general sphere of public international law.

Whereas, for example, Article 38(1)(b) of Statute of the International Court of Justice
expressly recognises the existence of customary international law as “evidence of a general practice accepted as law” is customary international law, on one interpretation of the Statute, one of several primary ‘sources’ of international law, or indeed, is it in actual fact the substance of international law itself? It is submitted that customary international law as evaluated and applied by the ICJ in cases before it, cannot be discussed in isolation of the disagreements surrounding the constitution and evolution of customary international law.

It must be further noted that a stark contrast exists as regards the law of States and public international law. Whereas in the municipal law of States legal doctrines and rules are developed and ‘fine-tuned’ so-to-speak, through constitutional institutions, legislative developments and the voluminous cases before the courts of that State, no such parallel law-making process or ‘all-powerful’ legislative body exists on the world forum. Thus, argues O’Connell, “Traditionally international law is customary law, for it is the product of the consciences of States and not the will of a political superior”.

The most fundamental principle underlying all customary international law then, is that of the sovereignty of the States. Taken to its most basic level the proposition of customary international law as being representative of an all-binding international law to be followed by States could be said to be no more than a collective legal fiction. In the end the absolute sovereignty of Nation-States to do as they will means that they are also free to disregard customary law if they so choose. This is not to say that there will be no repercussions as a consequence of such disregard of customary law, but that the possibility still exists.

It might however, be fair to say that the strength of customary international law has grown with the development and increased world membership of collective institutions. The original membership of the United Nations for example has increased from its 51 original members to 191 at present, thus increasing not only the power of enforcement of its decisions but of a communality of agreement through which collective treaties and international decisions have significantly contributed to the development of international norms and, in turn, customary international law.

Nevertheless it is the collective will of all States that gives life and force to this fiction. Following on from the establishment of a world forum through the creation of the UN in 1945, the world has experienced a globalisation of common aims, beliefs and values by States that has catalysed the development of international rules and norms. To this end States have ceded their sovereignty to help achieve such common goals. Thus, to speak of customary international law is to speak of a system of legal rules and norms that is adhered to by States by virtue not only of, for example, their social, economic, and political goals, but of their interdependence on other States and their belief in common aims such as international peace and security.

As such, customary international law can no longer be viewed as retaining a static foundation, but must be evaluated as a dynamic movement that is constantly evolving in response to the multilateral goals of States and of society as a whole. It is through this change that divergent attitudes towards customary law have developed. Brownlie thus notes that:

“Much of the traditional discussion of customary law suffers from the rigidity and narrow-mindedness of nineteenth-century positivism, which was itself the product of a static conception of society. The emphasis that the positivist places on the will of the State over-formalises the law and obscures its basic evolutionary tendency.”

In determining fundamental principles of justice underlying customary law the older and positivist-slanted interpretation of the system will not accept general principles of law deriving from the amalgamation of principles common to the laws of municipal states. Instead what is sought is positive evidence of the continued and aggregated actual practice of States alone. A naturalist take on customary international law however, will allow for the communality of principles of municipal and international law within a basic legal framework.

Within this framework viewed more as an international community than as a communality of government wills, international institutions and the judiciary play a significant role in developing customary international law. The consequence of this latter standpoint is all the more pertinent to a discussion of custom when one takes into account the increasing prominence played by human rights on the world stage.

In the South West Africa Cases (1966) Judge Kotaro Tanaka proffered the view that:

“The uniformity of national laws on the protection of human rights is not derived, as in the cases of the law of contracts and commercial and maritime transactions, from considerations of expediency by the legislative organs or from the creative power of the custom of a community, but it already exists in spite of its more-or-less vague form. This is of nature jus naturale in roman law.”

It is the reconciliation of these contrasting viewpoints that adds a further dimension to the “delicate and difficult” matter of customary international law. In order to develop a sound grasp of the notion of customary law a balance must be struck so “…one must take care to avoid the exaggerations of each of these respective positions, the one over-emphasising the content of the pattern of behaviour, the other the formalities of the law-making process.” The dangers of not doing so were summed up by one distinguished commentator when he stated that “…most of what we perversely persist in calling customary international law is not only not customary law: it does not even faintly resemble a customary law.”

The North Sea Continental Shelf Cases (1969) provide one of the few instances where the ICJ has provided a detailed analysis and overview of the existence and requirements of customary international law. In addition, the inherent difficulty of evaluating whether customary international law exists or not illustrated by Judge Tanaka’s opinion, as well as the varying positivist and naturalistic viewpoints, is revealed in the judgment of the Court

The case in actual fact consisted of two joined disputes relating to the delimitation of the continental shelves between the Federal Republic of Germany and Denmark and also between the Federal Republic of German and the Netherlands (“the Parties”). In general terms the continental shelf of a country is a continuation of the land mass but that extends beneath the sea with the width of the shelf ranging from one mile to hundreds of miles and varying in depth. The problem that presented itself in this case was that the German coast on the North Sea was ‘sandwiched’ between the coasts of Denmark and the Netherlands and thus the exact extent of the continental shelves of the respective Parties was open to debate. Thus, in submitting to the jurisdiction of the ICJ the Parties agreed to carry out the delimitation in accordance with what the Court judged the principles and rules of international to be.

Denmark and the Netherlands nevertheless argued that the “equidistance-special circumstances principle” which was widely acknowledged should apply to the delimitation whereas German believed that the delimitation should be carried out on the basis of the “doctrine of the just and equitable share”. If the delimitation were carried out according to the equidistance principle Germany would end up with a smaller continental shelf than would be allocated under the just and equitable share principle. The thrust of Denmark and the Netherlands’ arguments derived from the fact that they were parties to the 1958 Convention on the Continental Shelf (“the Convention”) and that Article 6(2) of the Convention stipulated the use of the equidistance principle if there was no agreement as to the delimitation of the continental shelves and “…unless another boundary line is justified by special circumstances” .

Nevertheless, Germany had signed but not ratified the Convention and therefore considered itself not legally bound by its terms. It therefore sought to argue that general principles of international law should dictate fairness and equity and that as a consequence, the doctrine of the just and equitable share was the most apt in the present case. Alternatively, it believed that even if the Convention were somehow held to apply to Germany, that owing to the geographical nature of the North Sea and the relative positioning of the States and the continental shelves, the special circumstances rule should be held to apply so as to give effect to the equitable share principle.

Whilst Denmark and the Netherlands conceded the fact that Germany had not ratified the Convention, they first sought to argue that “…by conduct, by public statements and proclamations, and in other ways, the Republic has unilaterally assumed the obligations of the Convention; or has manifested its acceptance of the conventional regime; or has recognized it as being generally applicable to the delimitation of continental shelf areas.”

The Court found that “…only a very definite, very consistent course of conduct on the part of a state in the situation of the Federal Republic” would justify these contentions. The viability of the Court’s pronouncement however, can be said to have been substantially hindered by its reasoning. Although it considered the possibility that the fundamental doctrine of estoppel could apply to evidence the contentions of Denmark and the Netherlands, it simply stated that there was no external evidence that this was so. The acceptance of a generalised doctrine of estoppel within international law evidenced a significant departure from the more fundamental requirements of positivist law-making. Nevertheless, the Court was content to reason on the basis that if Germany would have evinced acceptance of Article 6 by its past acts or conduct so as to evidence a situation of estoppel, why had it not signed the Convention? Furthermore, it added that in any event even if Germany had subsequently ratified the Convention it could just as easily have added a reservation to Article 6 since Article 12 of the Convention would have allowed it to do so.

The faulty reasoning demonstrated by the Court was highlighted by the Dissenting Opinion of Judge Tanaka. He believed that although a reservation might have been plausible in relation to the special circumstances clause, it was not possible in relation to the equidistance clause contained in Article 6(2). He stated that “…the reservation would in itself be null and void as contrary to an essential principle of the continental shelf institution which must be recognized as jus cogens. It is certain that this institution cannot properly function without being completed by some method of delimitation provided by law.

Consequently, it was submitted on the part of Denmark and the Netherlands that the provisions of Article 6 of the Convention had come to be regarded as customary international law. In his Dissenting Opinion Judge Tanaka’s reference to customary international law referred to what he considered to be the formative process of a customary law. More specifically Judge Tanaka regarded the formation of customary law as necessitating both a quantitative and a qualitative factor. He referred to the former as being the ‘corpus’ of customary law consisting of State practice being established through “a usage or continuous repetition of the same kind of acts”. In order for such State practice or usage to constitute a binding custom however, it required the presence of the latter qualitative factor, which Tanaka termed the ‘animus’, or more generally acknowledged as ‘opinion juris sive’ (a term which Mendelson sums up as “…a belief in (or claim as to) the legally permissible or obligatory nature of the conduct in question, or of its necessity”). As a corollary, Judge Tanaka noted that:

“To decide whether these two factors in the formative process of a customary law exist or not, is a delicate and difficult matter. The repetition, the number of examples of State practice, the duration of time required for the generation of customary law cannot be mathematically and uniformly decided. Each fact requires to be evaluated relatively according to the different occasions and circumstances.”

Thus, as regards the provisions of Article 6, the Court considered that treaties could come to be regarded as customary law in three forms. Firstly, a treaty could ‘crystallise custom’ through the collective agreement of States on the provisions of a treaty. Alternatively a treaty could declare existing custom through adoption of its provisions by States. Finally, subsequent States’ adoption, practice or following of a treaty’s provisions could come to represent custom.

The Court believed that Article 6 was not initially proposed by the International Law Commission as a rule of customary law. Moreover, since it permitted reservations to be made by States against this provision it could not be treated as a norm-creating provision and thus could not in any way be said to reflect or crystallise customary law. It further added that at that time although the Convention had been signed 10 years ago it had only been in force for 5 years and that when the proceedings had been initially brought before the Court the Convention was less than 3 years old. Whilst accepting in principle the possibility of a rapidly emergent international custom it considered that if this were to be the case:

“…an indispensable requirement would be that within the period in question, short though it might be, State practice, including that of States whose interests are specially affected, should have been both extensive and virtually uniform in the sense of the provision invoked; – and should moreover have occurred in such a way as to show a general recognition that a rule of law or legal obligation is involved.”

It did not believe this to be the case since even taking into account those States that were land-locked or to which the Convention was not open the number of States which had ratified or acceded to the provisions of the Convention could not be described as extensive and virtually uniform. Nor was subsequent State practice held by the Court to fulfil qualitative criteria. Alarmingly the Court was content to “presume” that those States “…acting unilaterally or conjointly, were… so far as they were concerned, acting actually or potentially in the application of the Convention” . The Court was not prepared to infer, or indeed enquire, if this was undertaken in furtherance of an obligation of customary law pertaining to the equidistance principle. Neither was it prepared to enquire into the actions of those States that were not a party to the Convention but had nevertheless followed the equidistance principle, dismissing their actions as simply being “problematical” and remaining “entirely speculative”.

Article 2 of the Convention was therefore held not to be customary law. The just and equitable share contention was also rejected on the basis that the continental shelf was a natural part of the land and was not subject to apportionment, since equity did not necessarily equate to equality. The Court’s final guidance was simply a statement of factors to which regard should be had when effecting an agreement on delimitation.

The reasoning of the Court from an overall perspective could be said to have been clouded from its need to fit the facts of the case to rigid perspectives of customary international law. This is exemplified, for instance, in the Dissenting Opinion of Judge Lachs which was more open to the reasoning behind the numbers of States and not simply a case of examining the number of parties to the Convention and the number of States in existence. To be entitled ‘customary law’ a principle did not have to be universally accepted. Furthermore, in his Dissenting Opinion Judge ad hoc Sørenson considered that the Court had failed to take into account the significance of the fact that the Convention was categorised as part of a series of multilateral treaties resulting from the development and codification of international law through the auspices of the United Nations. He therefore advocated a departure from the strictly positivist way of technical legal examination of the Convention and believed that the Convention should be interpreted within the context of a new dynamic of social, economic and technological development considerations.

The judgment of the Court was delivered by a margin of 11 votes to 6 with 5 cogent dissenting opinions annexed to the Judgment. It is therefore difficult to envisage how pronouncements by the Court on customary international law should be universally acknowledged without sound legal reasoning and such diversity of views. Sadly, the reasoning of the Court as regards customary international law is not much improved as evidenced by the case of Nicaragua v The United States (1986). There the Court again failed to demonstrate sound legal reasoning but instead attempted to fit the facts to the required legal rules and placed complete reliance on the subscription of States to UN resolutions. The case centred on whether the rule of non-intervention contained in Article 2(4) of the United Nations Charter formed customary law. Despite the fact that it found the practice of States was not “in absolutely rigorous conformity with the rule” it deemed instances of such conduct to be breaches of the rule and not evidence against the establishment of a custom. The actual independent practice of States in cases of, e.g. collective enforcement and humanitarian aid, was completely overlooked with subjective opinion juris nowhere to be seen.


BROWN, E.D., (1970), “The North Sea Continental Shelf Cases”. Current Legal Problems, Vol. 23, pp. 187-215;

BROWNLIE, IAN, (1979), “Principles of Public International Law” Clarendon Press Oxford (Third Edition).

D’AMATO, (1987) “Trashing Customary International Law” 81 American Journal of International Law 101 (1987)

DANILENKO, (1988) ‘The Theory of International Customary Law’, 31 German Yearbook of International Law (1988) 9.

HARRIS, D.J., (2004) “Cases and Materials on International Law” London Sweet & Maxwell (Sixth Edition)

INTERNATIONAL LAW ASSOCIATION (2000) — Committee on the Formation of Rules of Customary (General) International Law, Final Report of the Committee: Statement of Principles Applicable to the Formation of General Customary International Law (2000), See http://www.ila-hq.org/pdf/customarylaw.pdf.

KAMMERHOFER, JÖRG, (2004), “Uncertainty in the Formal Sources of International Law: Customary International Law and Some of Its Problems” EJIL (2004), Vol. 15 No. 3, 523–553.

O’CONNELL, D. P., (1970) “International Law” London Steven & Sons (Second Edition).

JENNINGS, R. Y., (1969), “The Limits of Continental Shelf Jurisdiction: Some Possible Implications of The North Sea Case Judgment” 18 I.C.L.Q. (1969), pp. 819-32.

MENDELSON, MAURICE, (1995) “The Subjective Element in Customary International Law” BYIL 66 (1995), 177.

ROBERTS, ANTHEA ELIZABETH, (2001) “Traditional and Modern Approaches to Customary International Law: A Reconciliation” The American Journal of International Law Vol. 95: pp. 747-791.

SHAW, MALCOLM N., (1997) “International Law”, Cambridge University Press, 4th Ed.

STONE, OLIVER L., “United States Legislation Relating to the Continental Shelf: With Especial Reference to the Exploitation of Oil and Gas Resources” 17 I.C.L.Q. (1968), pp. 103-117.

THE UNITED NATIONS, The Convention on the Continental Shelf, 1958.



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