On 23 September 2017, a Special Chamber of the International Tribunal for the Law of the Sea (the ‘Tribunal’) delivered its Judgment in the Dispute Concerning Delimitation of the Maritime Boundary between Ghana and Côte d’Ivoire in the Atlantic Ocean.[1] The case concerned the interpretation of provisions of the 1982 United Nations Convention on the Law of the Sea concerning the delimitation of the territorial sea, exclusive economic zone (‘EEZ’) and the continental shelf between Ghana and Côte d’Ivoire in a disputed area of the Atlantic Ocean.

The proceedings were initially instituted by Ghana under Article 287 and Annex VII to the Convention on 19 September 2014. The Parties subsequently agreed on 3 December 2014 to submit the dispute to a Special Chamber of the Tribunal established under Article 15 of Annex VI to the Convention.

The Judgment is significant for being only the second in which an international court or tribunal has delimited a continental shelf boundary between States beyond 200 nautical miles, and also provides a useful illustration of the application of the equidistance/relevant circumstances methodology of delimitation increasingly favoured by international courts and tribunals.

Customary Equidistance Boundary

Ghana had sought at the outset to characterise the dispute as relating to the existence of a ‘customary equidistance boundary’, and not as a traditional boundary delimitation case, arguing that a tacit agreement had emerged through decades of practice accepted by both States. Ghana relied in particular on the offshore oil activity carried out or authorised by both States, with supplementary reliance placed upon oil concession and other maps produced by both States and national legislation. This was disputed by Côte d’Ivoire, which maintained that it had distinguished between oil activity and the issue of the maritime boundary, and that it had acted with prudence and caution in order not to prejudice efforts to reach an agreement on a maritime boundary. It also maintained that it had recently objected to some oil activities carried out or authorised by Ghana in the disputed area.

The Tribunal highlighted that evidence of a tacit agreement to a maritime boundary had to be compelling,[2] and although it was undisputed that the line invoked by Ghana had been relevant to both States in the conduct of their respective oil activities over a long period of time, this was insufficient to establish the existence of a maritime boundary, since it could be explained by other reasons including the exercise of caution by the Parties.[3] The Tribunal also explained that evidence of oil activity was of limited value in proving the existence of an all-purpose boundary.

Delimitation Methodology

Although both States had agreed that the same delimitation methodology should be used for the whole delimitation process, there was disagreement concerning the method to be applied. Ghana argued that the equidistance/relevant circumstances method should be used as it represented the standard method of delimitation in international jurisprudence. Côte d’Ivoire argued that the angle-bisector method represented the most appropriate method, particularly in view of the geography of the area and the interests of neighbouring States. The Tribunal emphasised that the goal of achieving an equitable result was the paramount consideration and that in the absence of any compelling reasons making it impossible or inappropriate to draw a provisional equidistance line, the equidistance/relevant circumstances method should be chosen for maritime boundary delimitation. The Tribunal went on to apply the ‘internationally established’ three-stage approach favoured by international courts and tribunals in the majority of recent boundary delimitation cases.[4]

At the first stage, the Tribunal considered the charts to be used as the basis for the delimitation. Ghana sought to rely upon official charts that had been used by both parties until 2014, whereas Côte d’Ivoire relied upon a new chart that it had commissioned at considerable cost using satellite-derived bathymetry. The Tribunal was unwilling to use the Côte d’Ivoire chart, and referred instead to the older official charts, [5] noting that the chart relied upon by Côte d’Ivoire had been prepared using different methods to survey the coasts of Côte d’Ivoire and the coasts of Ghana respectively and so could not be used.

The Tribunal then proceeded to identify the starting point of the maritime boundary, and determined a suitable point by following the course of the agreed land boundary until it reached the low-water line at a point referred to as BP 55+ (see diagram below).[6] After identifying the relevant coasts and coastal projections, the Tribunal constructed a provisional equidistance line using base points selected from official charts identified by the Tribunal. At the second-stage, the Tribunal found that there were no relevant circumstances that would justify an adjustment to the provisional line.[7] At the final stage, the Tribunal applied the ‘disproportionality test’ and verified that the provisional line did not lead to an inequitable result owing to any marked disproportion between the ratio of the respective coastal lengths and the ratio of the relevant maritime area allocated to each Party.[8]

Continental Shelf Delimitation Beyond 200 Nautical Miles

Both States had agreed that the Tribunal could delimit the continental shelf boundary beyond 200 nautical miles without prejudice to submissions each State had lodged with the Commission on the Limits of the Continental Shelf (‘CLCS’) for the purposes of establishing the outer limits of the continental shelf beyond 200 nautical miles under Article 76 of the Convention.

The Tribunal reaffirmed the position it adopted in the 2012 Bangladesh/Myanmar case, where it distinguished between the delimitation of the continental shelf and the determination of the outer limits. This enabled the Tribunal to delimit the continental shelf between States without conflicting with the role and functions of the CLCS concerning the establishment of the outer limits. As both States had made submissions to the CLCS and Ghana had received affirmative recommendations from the CLCS, the Tribunal had no doubt that continental shelf beyond 200 nautical miles existed in respect of both States[9] .

With respect to the method of delimitation, the Tribunal considered that the delimitation method to be applied to the continental shelf beyond 200 nautical miles should not differ from the method adopted in respect of the continental shelf within 200 nautical miles. On that basis, the Tribunal proceeded to apply the equidistance/relevant circumstances method to extend the line of the single maritime boundary beyond 200 nautical miles until it reached the outer limits of the continental shelf.[10] The diagram below illustrates the disputed area and the single maritime boundary determined by the Tribunal.


In a Joint Communique issued on 17 October 2017, the Leaders of Ghana and Côte d’Ivoire announced the establishment of a Joint Committee for the Implementation of the ITLOS judgment and indicated that the composition of the Committee would be decided at a later date.