Tullow announced Monday it encountered more than 65 feet of net oil pay at its Ngamia-1 exploration well in Kenya.
Tullow Exploration Director Angus McCoss described the discovery as "an excellent start" to its campaign in Kenya.
"To make a good oil discovery in our first well is beyond our expectations and bodes well for the material program ahead of us," he said in a statement.
Ian Cloke, Tullow's exploration manager for East Africa, said at an energy conference in Nairobi there were more things to come.
"We are pretty confident there is further potential as we drill down," he was quoted by Bloomberg News as saying.
Tullow said it was investing $428 million in its exploration campaign in East Africa.
Kenyan President Mwai Kibaki said Tullow's discovery marked "the beginning of a long road to make our country an oil producer."