Under terms of the agreement, Roc has the right to jointly appraise potential acquisitions identified by Osprey and to directly co-invest with Osprey on an unprompted, 50:50 basis in "appropriate opportunities", Roc told the market.

Osprey is largely Africa-focused and is managed by founder directors John Bently and Jim Rutland, who were previously in charge of Energy Africa, a South African company with interests in nine African countries.

Roc already has a small stake in a Woodside joint venture in Mauritania and a much larger stake in the fast-growing oil province off Equatorial Guinea. It also has exploration territory in Angola.

Roc acquired the stake along with four international financial institutions as part of a wider participation agreement. They are the International Finance Corporation, African Merchant Bank, RMB Resources and the Standard Bank London.

In other Roc news, the company said its exploration and appraisal drilling program was "on track" with between eight and 20 wells to be drilled in five countries over the next 12 months.

"Two of the first three wells in this program have encountered potentially commercial hydrocarbons offshore Mauritania, as evidenced by gross hydrocarbon columns of 94m and 133m," the company said.