British oil and gas company Afren said the Ebok-6 appraisal well, located off the coast of Nigeria, has exceeded pre-drill expectations, raising estimates for the field.
The company said that Ebok-6 encountered a total of 107ft of gross oil pay.
"We have significantly upgraded reserves at the project to 116m barrels recoverable, representing an incremental 91m barrels recoverable, through a 100% drilling success rate," said Afren chief executive Osman Shahenshah.
Shares in Afren at one point rose by 7.2% to their highest level since September 2008, reports Reuters.
Afren moved up to the main market in December from London's junior AIM market and the shares are expected to be included in the FTSE 250 Index in the next reshuffle.