North Sea Continental Shelf Cases (Federal Republic of Germany v Denmark; Federal Republic of Germany v Netherlands)

• Germany, Denmark, and the Netherlands disputed the delimitation of continental shelf boundaries in the North Sea
• Denmark and the Netherlands argued that the equidistance principle in Article 6 of the 1958 Geneva Convention had become customary law
• Germany had signed but not ratified the 1958 Convention
• The equidistance method would give Germany a disproportionately small continental shelf area due to the concavity of its coastline
• Germany argued delimitation should be based on equitable principles

1. Whether Article 6 of the 1958 Geneva Convention on the Continental Shelf (the equidistance principle) had become a rule of customary international law binding on Germany, which had not ratified the Convention.

• Article 6 had not crystallised into customary international law
• For a treaty rule to become custom, it must be norm-creating in character (capable of general application)
• State practice must be widespread, representative, and include specially affected states
• Practice must be accompanied by opinio juris sive necessitatis (belief that the practice is legally obligatory)
• Short duration of practice does not bar crystallisation, but density and uniformity are essential

Not all treaty provisions are capable of forming the basis of a general rule of law. Only provisions of a fundamentally norm-creating character can crystallise into customary rules. Two conditions must be fulfilled: there must be very widespread and representative participation in the practice, including specially affected states; and the practice must be carried out in such a way as to evidence a belief that this practice is rendered obligatory by the existence of a rule of law requiring it (opinio juris).