International Court of Justice — Chamber — Frontier dispute between Benin and Niger — Parties jointly submitting dispute to Chamber of Court by Special Agreement — Parties seeking definitive delimitation of whole boundary — Parties requesting Court to specify ownership of islands, in particular Lété Island — Boundary divided into two sectors — Determination of course of boundary in River Niger sector — Ownership of islands in River Niger, in particular Lété Island — Determination of course of boundary in River Mekrou sector — Article 2(a), (b) and (c) of Special Agreement — Applicable law — Rules and principles of international law — Article 38(1) of Statute of International Court of Justice — Principle of uti possidetis juris — Article 6 of Special Agreement

Territory — Sovereignty — Boundary between Benin and Niger — River Niger sector — Delimitation on basis of uti possidetis juris principle — Benin and Niger former colonies of French West Africa — Benin and Niger becoming independent on 1 and 3 August 1960 respectively — Determination of boundary inherited from French administration on 1 and 3 August 1960 — Critical date — French colonial law — Cartographic and other evidence — Relevance — Main navigable channel of River Niger at dates of independence — Colonial boundaries becoming international frontiers upon independence — Whether evidence of title on basis of colonial regulative or administrative acts — Legal relationship between effectivités and title — Effectivités — Determination of precise location of boundary line in main navigable channel of River Niger at dates of independence — Article 2(a) of Special Agreement

Territory — Sovereignty — Islands in River Niger sector — Island of Lété — Determination of boundary in River Niger — Consequent title to islands — Appearance or disappearance of islands — Whether determination of ownership of islands prejudicing private law rights — Article 2(b) of Special Agreement

Territory — Sovereignty — Boundary between Benin and Niger — Bridges — River Niger sector — Niger requesting determination of boundary on two bridges between Gaya and Malanville — Whether Chamber having jurisdiction to determine boundary on bridges — Whether any finding prejudicing joint ownership of bridges — Whether prejudicing arrangements regarding use and maintenance — Article 2(a) of Special Agreement

Territory — Sovereignty — Boundary between Benin and Niger — River Mekrou sector — Delimitation on basis of uti possidetis juris principle — Benin and Niger former colonies of French West Africa — Benin and Niger becoming independent on 1 and 3 August 1960 respectively — Critical date — Determination of boundary inherited from French administration on 1 and 3 August 1960 — Examination of legal titles — French colonial law — Cartographic and other evidence — Relevance — Interpretation and application of legal titles by colonial administrative authorities — Effectivités — Relevance — Exact location of boundary — Whether boundary following course of thalweg or median line of River Mekrou — Article 2(c) of Special Agreement

State succession — Colonies — States in western Africa — Benin and Niger formerly part of French West Africa — Benin formerly colony of Dahomey — Governor-General of French West Africa having power to determine boundaries of colonies — Benin becoming independent on 1 August 1960 — Niger becoming independent on 3 August 1960 — Critical date — States succeeding to frontiers inherited from colonialism — Intangibility of frontiers — Principle of uti possidetis juris — Boundary between Benin and Niger on dates of independence