For a long time, Ghana believed that there was a de facto maritime boundary line between Ghana and Côte d’Ivoire, and since the 1950s had conducted hydrocarbon activities based on its understanding of this ‘customary boundary’. Côte d’Ivoire, for its part, was not particularly active in protesting Ghana’s hydrocarbon activities. Only in 2009 did Côte d’Ivoire make a proposal as to its view of the maritime boundary thus forming a triangular area of overlapping maritime claims. The area claimed by Côte d’Ivoire covered significant oil and gas fields discovered by Tullow Oil plc operating under a license of Ghana. Ghana alleged that this was the main reason why Côte d’Ivoire raised its claims.
Yiallourides, C., & Ermolina, N. (2017). State Responsibility for Unilateral Hydrocarbon Activities in Disputed Maritime Areas: The case of Ghana and Côte d’Ivoire and its implications. The blog of the Norwegian Centre for the Law of the Sea. https://site.uit.no/nclos/2017/11/23/state-responsibility-for-unilateral-hydrocarbon-activities-in-disputed-maritime-areas-the-case-of-ghana-and-cote-divoire-and-its-implications/