Sterling Energy is to withdraw from the Block C-3 joint venture, offshore Mauritania.
The move will see Tullow Oil take over Sterling's 40.5% share in the production sharing contract (PSC) for Block C-3.
Upon completion, the holders of the PSC will be: Tullow (Operator) 90%; Société Mauritanienne des Hydrocarbures et de Patrimoine Minier 10%.
The PSC, awarded in 2013, covers about 9800sq km. In 2014, Tullow acquired 1600km of 2D seismic.
"Following receipt of the processed regional 2D seismic (comprising about 1854 line kms), the company is of the view that the 2D seismic data has not sufficiently de-risked the block potential, to justify Sterling entering into Phase 2 of the PSC in June 2016," says Sterling.
Phase 2 includes a minimum work obligation of 700sq km of 3D seismic and drilling one well.
Sterling retains its interest in Block C-10, offshore Mauritania, also operated by Tullow and on which a well is planned for 2017.
Eskil Jersing, Sterling's CEO, said: "In our opinion the newly acquired and processed regional 2D seismic has not sufficiently de-risked Block C-3 to enable Sterling to commit to enter into Phase 2 of the PSC due to begin in June 2016."