The Republic of Ghana and the Republic of Côte d'Ivoire agreed to submit to a Special Chamber of the International Tribunal for the Law of the Sea a dispute concerning the delimitation of their maritime boundary in the Atlantic Ocean.

Ghana argued that it and Côte d’Ivoire have mutually recognised, agreed, and applied an equidistance-based maritime boundary in the territorial sea, EEZ and continental shelf within 200 nm. The maritime boundary in the continental shelf beyond 200 nm follows an extended equidistance boundary along the same azimuth as the boundary within 200 nm, to the limit of national jurisdiction. In accordance with international law, by reason of its representations upon which Ghana has placed reliance, Côte d’Ivoire is estopped from objecting to the agreed maritime boundary.

Côte d’Ivoire disagreed, arguing that the maritime boundary follows the 168.7° azimuth line, which starts at boundary post 55 and extends to the outer limit of the Ivorian continental shelf. Activities undertaken unilaterally by Ghana in the Ivorian maritime area therefore constituted a violation of the exclusive sovereign rights of Côte d’Ivoire over its continental shelf. Côte d’Ivoire also contended that Ghana had failed to negotiate in good faith, pursuant to art 83.1 of UNCLOS and customary law, had breached the obligation not to jeopardise or hamper the conclusion of an agreement, as provided for by art 83.3 of UNCLOS, and had violated the provisional measures prescribed by the Chamber by its Order of 25 April 2015. Côte d’Ivoire therefore sought disclosure of all the documents and data relating to the oil exploration and exploitation activities which Ghana has undertaken in the Ivorian maritime area, and compensation for the damages caused to it by Ghana's internationally wrongful acts.

Held: The Special Chamber:
(1) Unanimously finds that it has jurisdiction to delimit the maritime boundary between the Parties in the territorial sea, in the exclusive economic zone and on the continental shelf, both within and beyond 200 nm;
(2) Unanimously finds that there is no tacit agreement between the parties to delimit their territorial sea, exclusive economic zone and continental shelf both within and beyond 200 nm, and rejects Ghana’s claim that Côte d’Ivoire is estopped from objecting to the 'customary equidistance boundary';
(3) Unanimously determines the single maritime boundary for the territorial sea, the exclusive economic zone and the continental shelf between the parties;
(4) Unanimously finds that it has jurisdiction to decide on the claim of Côte d’Ivoire against Ghana on the alleged international responsibility of Ghana;
(5) Unanimously finds that Ghana did not violate the sovereign rights of Côte d’Ivoire;
(6) Unanimously finds that Ghana did not violate arts 83.1 and 83.3 of UNCLOS; 
(7) Unanimously finds that Ghana did not violate the provisional measures prescribed by the Special Chamber in its Order of 25 April 2015.

The present dispute concerns the interpretation and application of the relevant provisions of UNCLOS, in particular arts 15, 74, 76 and 83. The parties agree that the Special Chamber has jurisdiction to adjudicate on the dispute submitted by the Special Agreement concerning the delimitation of the territorial sea, the exclusive economic zone and the continental shelf.

In respect of Ghana's argument that there is a 'tacit agreement' on delimitation, the factual evidence suggests no specific arrangements between the parties on fisheries or other maritime matters. Although it appears that the parties follow an equidistance line in their fishing activities, there is no evidence to suggest that the Parties recognise that line as their fishery or maritime boundary. The other maritime activities of the parties fall short of proving the existence of any agreed maritime boundary between them. As the ICJ observed in Territorial and Maritime Dispute between Nicaragua and Honduras in the Caribbean Sea (Nicaragua v Honduras): 'Evidence of a tacit legal agreement must be compelling. The establishment of a permanent maritime boundary is a matter of grave importance and agreement is not easily to be presumed'.

As to Ghana’s alternative argument of estoppel, this is essentially based on the same facts put forward by it to establish the existence of a tacit agreement. Côte d’Ivoire has not demonstrated, by its words, conduct or silence that it agreed to the maritime boundary based on equidistance. It is true that Côte d’Ivoire’s oil concession blocks align with those of Ghana along the equidistance line and that Côte d’Ivoire’s oil activities do not cross over into the Ghanaian side of the equidistance line. However, Côte d’Ivoire has taken care to indicate that the limits of its oil concession blocks are distinct from those of its maritime jurisdiction. It also has expressed its concern to Ghana about the continuation of oil activities in the area yet to be delimited. Therefore, the conduct of Côte d’Ivoire cannot be considered to amount to the 'clear, sustained and consistent' representation required for the recognition of estoppel.

The Special Chamber then applied the three-stage equidistance/relevant circumstances/disproportionality methodology to delimit the maritime boundary between the parties.

In a case of overlap both coastal States concerned have an entitlement to the relevant continental shelf on the basis of their relevant coasts. Only a decision on delimitation establishes which part of the continental shelf under dispute appertains to which of the claiming States. This means that the relevant judgment gives one entitlement priority over the other. Such a decision accordingly has a constitutive nature and cannot be qualified as merely declaratory. The consequence of the above is that maritime activities undertaken by a State in an area of the continental shelf which has been attributed to another State by an international judgment cannot be considered to be in violation of the sovereign rights of the latter if those activities were carried out before the judgment was delivered and if the area concerned was the subject of claims made in good faith by both States. As a consequence, Ghana's previous hydrocarbon activities did not violate the sovereign rights of Côte d’Ivoire.