Royal Dutch Shell has teamed up with Tullow Oil to find major new fields in the Atlantic.
Tullow said the partnership would seek "transformational" discoveries in "underexplored frontier basins".
The deal adds to the company's tie-ups, which include exploration partnerships with Anadarko Petroleum, Statoil, Total and Cnooc.
It plans to drill about 40 exploration and appraisal wells this year.
However, Tullow's shares still slipped 4 per cent to 1,394p yesterday, as it also flagged a decline in production in its trading update ahead of its full-year results in March.