CNOOC Ltd gave up most of its stake in a Nigerian oil block even after making two discoveries, Reuters reported, citing an unidentified person familiar with the situation.

CNOOC, China's third-biggest oil and gas firm, agreed earlier this month to relinquish a 35-percent stake to Emerald Energy Resources Ltd, the Nigerian operator of the oil block. CNOOC will retain a 5-percent stake to be used as collateral for an US$80 million loan to the project, Reuters reported.