Africa-focused energy company Tullow Oil said it made its most significant find yet in a northern Kenyan reserve area not previously known to hold oil.

Tullow said it found good samples of oil in the cores taken from a well in the so-called Cheptuket-1 well in the Kerio Valley basin in northern Kenya. Dubbed a wildcat well, or a frontier area not previously known to contain oil, the company said it was its most significant find yet in the region.

"I am delighted by this wildcat well result and the team is already working on our follow-up exploration plans for the Kerio Valley basin," Tullow Exploration Director Angus McCoss said in a statement.

The company in November came up empty-handed while drilling into similar frontier basins in northern Kenya, despite early optimism.

Tullow, which has headquarters in London, is placing bets on emerging basins in Africa, notably offshore developments in Ghana. Few commercial developments have been reported in the region and low oil prices may inhibit substantial investments, a market scenario that's encouraged multi-party development deals.

Tullow, which focuses almost exclusively on African basins, reported a drop in revenue of around 27 percent and a net debt increase of around $4 billion for 2015.