On 23 September 2017, a Special Chamber of the International Tribunal for the Law of the Sea (ITLOS) delivered its judgment on the longstanding maritime boundary dispute between Ghana and Côte d’Ivoire.

The Special Chamber reconfirmed the relevance of the equidistance methodology in determining the maritime boundary between the two States. The judgment also touches on important issues affecting States and international companies operating in disputed waters such as the applicable obligations pending resolution of such disputes.


The dispute between Ghana and Côte d’Ivoire arose following the discovery of hydrocarbon resources off their coasts, and which both claimed were within their jurisdiction.

On 19 September 2014, Ghana instituted arbitration proceedings under Annex VII of the UN Convention on the Law of the Sea (UNCLOS), requesting ITLOS to delimit the maritime boundary between Ghana and Côte d’Ivoire in the Atlantic Ocean. Following negotiations in December of the same year, the two States agreed for the dispute to be submitted to a special chamber of ITLOS (the “Special Chamber“). The Special Chamber was comprised of three permanent judges of ITLOS: Vice-President Bouguetaia, Judges Wolfrum and Paik, and two ad hoc judges, Judges Mensah and Abraham.

On 25 April 2015, following a request by Côte d’Ivoire for the prescription of provisional measures, the Special Chamber ordered, pending its final decision, that Ghana take all necessary steps to ensure that no new drilling take place in the disputed area (the “25 April 2015 Order“).

The hearing took place between 6 and 16 February 2017, and on 23 September, the Special Chamber handed down its unanimous judgment, delimiting the maritime boundary between Ghana and Côte d’Ivoire, and rejecting all other claims made by Côte d’Ivoire against Ghana.

Relief sought by both States

Ghana sought from the Special Chamber a finding and declaration that:

  • Ghana and Côte d’Ivoire have mutually recognised, agreed and applied an equidistance-based maritime boundary in the territorial sea, exclusive economic zone (EEZ) and continental shelf within 200NM; and
  • Côte d’Ivoire be estopped from objecting to this boundary, by reason of representations it had made to this effect and on which Ghana had relied.

Côte d’Ivoire, in turn, requested that the Special Chamber reject all of Ghana’s claims and find instead that:

  • the maritime boundary between Ghana and Côte d’Ivoire follows a determined azimuth line from geographic coordinates provided by Côte d’Ivoire to the outer limit of the Ivorian continental shelf (arguing in favour of the application of the angle bisector methodology in determining the boundary);
  • activities already undertaken by Ghana in the Ivorian maritime area constitute a violation of Côte d’Ivoire’s exclusive sovereign rights over its continental shelf, and a violation of the 25 April 2015 Order; and
  • Côte d’Ivoire is entitled to compensation for damages resulting from Ghana’s violation of Côte d’Ivoire’s exclusive sovereign rights over its continental shelf.

The Parties’ submissions and the Special Chamber’s ruling

  1. Tacit agreement and estoppel

The Special Chamber rejected Ghana’s claims that there was a long-standing tacit agreement between both Parties that the “principle of equidistance” applied to the delimitation of their maritime boundary, and that this boundary had been recognized and respected over a period of over 5 decades.

Ghana, in advancing this claim, had sought to rely on concession agreements, presidential decrees, legislation, correspondence, oil concession and other maps, public statements, and representations made by both States to international organisations and oil companies. Côte d’Ivoire, in turn, denied the existence of any such agreement, whether formal or tacit.

The Special Chamber found that the oil concession maps, legislation and decrees put forward by Ghana did not authoritatively define a maritime boundary in the relevant area. In addition, it found that the bilateral exchanges and negotiations which had taken place between the parties from 1988 to 2014 indicated that no tacit agreement had been reached between the parties on the delimitation of their maritime boundaries. The Special Chamber noted that Ghana’s arguments of estoppel were essentially based on the same facts as those put forward by it to establish a case of tacit agreement. It found that Ghana had failed to demonstrate that an agreement to the maritime boundary based on equidistance existed, or that the requirements for estoppel had been met.

  1. Delimiting the maritime territorial boundary

Ghana requested that the delimitation of the territorial sea be based on the application of the equidistance methodology, relying on article 15 of UNCLOS, which states that the equidistance principle will apply except “where it is necessary by reason of historic title or other special circumstances to delimit the territorial seas of the two States in a way which is at variance therewith.

Côte d’Ivoire, invoking special circumstances (in particular the concavity of the Ivorian coast and the instability of the coastline), argued in favour of the application of the angle bisector methodology for the delimitation of the territorial sea, EEZ and the continental shelves.

The Special Chamber noted that the delimitation of the territorial sea is governed by article 15 of UNCLOS, which favours the application of the equidistance principle to delimit maritime boundaries where the coasts of two States are opposite or adjacent to each other, save where historic title or other special circumstances justify using an alternative methodology. The Special Chamber found that Côte d’Ivoire had failed to provide sufficient evidence that special circumstances justified using an alternative methodology to determine the maritime boundary in this instance. It ruled that the equidistance methodology should be applied in this case and proceeded to delimit the maritime boundary of the territorial sea, the EEZ and the continental shelf applying this methodology.

The parties were agreed that the equidistance methodology involved three stages, which the Special Chamber applied in turn when delimiting the boundary.  First, a provisional equidistance boundary line was constructed.  Second, the Special Chamber considered whether that line should be adjusted to take into account any relevant circumstances (the Special Chamber rejected all such relevant circumstances proposed by the parties, and did not adjust the provisional line), and finally, the line was reviewed to confirm it did not result in a gross disproportionality between the parties’ relevant coasts and maritime areas (the Special Chamber concluded it did not).

  1. Ghana’s international responsibility

The Special Chamber then went on to consider the issues of the international responsibility of Ghana, in particular whether Ghana had violated:

  • Côte d’Ivoire’s sovereign rights by conducting or licensing hydrocarbon activities in an area claimed by Côte d’Ivoire;
  • articles 83(1) and (3) of UNCLOS (requiring parties to a maritime boundary dispute to negotiate in good faith to reach an agreement and to avoid taking any measures which may jeopardize or hamper the reaching of such an agreement); and
  • the 25 April 2015 Order.

In support of its claim, Côte d’Ivoire referred to “three unchallenged foundations” of its argument on sovereign rights, namely that (i) “the rights pertaining to the exploration and exploitation of the continental shelf are exclusive rights“, (ii) “those rights exist ipso facto and ab initio“, and (iii) the delimitation by the Special Chamber does not create such rights, but merely clarifies their scope (in effect, arguing that the judgment would be of a declaratory nature). It further argued that the inherent character of sovereign rights meant that the exclusive rights to the continental shelf could be violated by Ghana through its earlier activities even when the delimitation line was still to be defined. Ghana did not seek to deny that a delimitation was declaratory, but rather claimed that its activities had not violated Côte d’Ivoire’s sovereign rights. It claimed that its activities in the disputed area had never been unilateral. They were conducted openly, with Côte d’Ivoire’s cooperation and implicit consent. Ghana further maintained that the courts and tribunals in this context “have consistently declined to punish a State for good-faith use of territory which is ultimately awarded to its neighbour“.

The Special Chamber agreed with the statements of the two Parties that the sovereign rights which coastal States enjoy in respect of the continental shelves off their coasts are exclusive in nature. Significantly, however, the Special Chamber disagreed with both Parties as to the meaning of a judgment on the delimitation of a continental shelf, and in particular with their arguments that such judgments are only of a declaratory nature. The Special Chamber found otherwise, noting that “[o]nly a decision on delimitation establishes which part of the continental shelf under dispute appertains to which of the claiming States. […]Such a decision accordingly has a constitutive nature and cannot be qualified as merely declaratory“. In the view of the Special Chamber, 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 (i) those activities were carried out before the judgment was delivered, and (ii) the area concerned was the subject of claims made in good faith by both States. Accordingly, even assuming that certain hydrocarbon activities carried out by Ghana had taken place in areas attributable to Côte d’Ivoire following the delimitation, the Special Chamber found that those activities would not have constituted a violation of the sovereign rights of Côte d’Ivoire. Ultimately, however, the Special Chamber was clear that Ghana had in fact only undertaken hydrocarbon activities in an area attributable to it.

The Special Chamber similarly concluded that Ghana’s conduct was not in violation of Articles 83 (1) and (3) of UNCLOS as negotiations regarding the maritime boundary had been conducted in good faith between both States. It also found that Ghana had complied with the 25 April 2015 Order by ensuring that no new drilling took place in the disputed area (although it noted that it would have been preferable had Ghana done so earlier).


The Special Chamber’s judgment will no doubt be of interest to international law specialists, States, and international oil companies conducting activities close to disputed maritime borders. Of particular interest are the following findings:

  • The Special Chamber’s finding that its judgment on delimitation was constitutive (or forward-looking), not merely declaratory (or backwards-looking). This did not have an immediate impact in this case because the activities conducted by Ghana took place in what, following the delimitation, was part of Ghana’s maritime area. However, the decision raises the possibility that States conducting drilling and exploration activities in disputed areas later delimited as falling within another State’s maritime area have not breached the other State’s rights, or international law.  While this might appear to encourage States to seek to exploit resources prior to any determination being made, it remains notable that the Special Chamber qualified its judgment to the effect that a State engaging in such activities would not be considered in violation of the sovereign rights of the other State, provided the area concerned was the subject of claims “made in good faith by both States“.
  • The Special Chamber’s analysis of the two obligations under Article 83 (3) of UNCLOS, namely to “make every effort to enter into provisional arrangements of a practical nature” and “during this transitional period, not to jeopardize or hamper the reaching of the final agreement“, is also of significance in this context.
    1. The Special Chamber noted that the obligation to engage in negotiations in good faith to enter into provisional arrangements pending the resolution of the dispute was an obligation of conduct, not of result. In this case, the Special Chamber placed the onus on Côte d’Ivoire to request that Ghana put in place provisional arrangements. Côte d’Ivoire’s failure to request that Ghana enter into negotiations on provisional arrangements was found to constitute a bar to it claiming that Ghana had violated its obligations to negotiate on such arrangements. As such, the primary responsibility of commencing the relevant negotiations would seem to be on the State contesting the use of the disputed waters.
    2. The Special Chamber did not provide guidance on what type of arrangements would need to be taken to comply with the latter obligation not to jeopardize or hamper the reaching of a final agreement. It limited itself instead to a finding that the obligation had been complied with in this instance as (i) Ghana had complied with the 25 April 2015 Order, and (ii) Ghana had only undertaken hydrocarbon activities in an area ultimately attributable to it. Judge Paik in his separate opinion, however, noted his “serious reservation about the lawfulness of Ghana’s activities in the disputed area” under Article 83(3) and found the reasons given by the Special Chamber in support of its conclusion “insufficient and unconvincing“. Judge Paik clarified that, in his view, the obligation was result-orientated, and a key consideration was whether the activities in question would have the effect of endangering the process of reaching a final agreement or impeding the progress of negotiations. In this respect, the “type, nature, location and time of acts as well as the manner in which they are carried out may be relevant“.

For more information, please contact Andrew Cannon, Partner, Iain Maxwell, Of Counsel, Maguelonne de Brugiere, Senior Associate, or your usual Herbert Smith Freehills contact.

Andrew Cannon
Andrew Cannon
+33 15 357 6552
Iain Maxwell
Iain Maxwell
Of Counsel
+44 20 7466 2646
Maguelonne de Brugiere
Maguelonne de Brugiere
Senior Associate
+81 354 125 457