Sea — Maritime boundaries — Delimitation — Arbitral tribunal asked to decide whether agreement concluded by colonial powers in force between successor States — Agreement only effecting delimitation of maritime areas existing at time concluded — Relevance of customary international law

State succession — Treaties — Agreement concluded by colonial powers regarding maritime delimitation — Whether binding upon successor States — Effect of declaration of tabula rasa on agreement

State succession — Boundaries — Principle of uti possidetis — Whether applicable to maritime boundaries — Principles of sovereignty over natural resources — Effect on maritime delimitation agreement concluded by colonial powers — Liberation movement operating in colony — Whether restricting authority of colonial power to conclude treaties in respect of colony

Arbitration — Arbitration agreement — Maritime boundary delimitation — Competence of tribunal — Arbitration agreement concluded by States not party to agreement which formed subject-matter of arbitration — Competence of tribunal in respect of earlier agreement

Treaties — Validity — Effect of breach of internal law on validity of treaties — Relevance of practice in assessing whether breach of internal law renders treaty invalid — Effect of non-registration of treaty with United Nations — Franco-Portuguese exchange of letters, 1960 — Article 46 of the Vienna Convention on the Law of Treaties