Tullow announced that oil was encountered at its Enyenra-3A well in its Tana license off the coast of Ghana. Pressure data indicated there was a continuous oil column of at least 1,197 feet.
The company's drillship encountered the reserve after drilling in water depths of more than 3,600 feet.
Tullow Oil and its partners in Ghana marked a milestone for the Jubilee oil field last December when commercial oil flowed from the area for the first time. The company said that production there could increase to 120,000 bpd.
Ghana is looking for experts to develop its offshore potential, as the newly elected government has little experience in managing oil reserves. The Jubilee field is one of the richest oil fields in Africa with potential reserves eclipsing 1.8 billion barrels.
Oxfam International had said there were transparency concerns regarding oil laws in Ghana.