LONDON — No commercially exploitable oil had been discovered in Kenya until Tullow Oil began drilling this year in the blazing savanna of the Rift Valley, about 250 miles northwest of Nairobi.

In May, the company said that its first well had produced promising results, finding more oil-bearing sands than wells drilled in the geologically similar Lake Albert region of Uganda, where Tullow discovered a 1.1-billion-barrel field in 2006.

If Kenya turns out to be another Uganda, Tullow will have been instrumental in opening up no fewer than four new oil basins in the last six years. Three, including the jumbo-size Jubilee field in the deep waters off Ghana, are in sub-Saharan Africa. The fourth, off French Guiana in South America, was the payoff of a bet that the same oil-bearing rocks found in West African waters would also be present off the coast of Latin America.

Is it luck? Competitors do not think so. “On their track record — you have to say it is really good,” said Neil Piggott, a longtime explorer, who now heads exploration in Brazil for BP.