British energy explorer Tullow Oil said Thursday it was reviewing options at its oil basins in Kenya after encountering extensive reserves in shale.

Tullow said Thursday it ran into a 200-foot column of oil while drilling into its Twiga-2 appraisal well. At least 16 feet of oil was encountered during drilling operations at the company's Ekunyuk-1 well in northern Kenya.

"The presence of a thick extensive oil shale gives us new options to study the basin's substantial unconventional oil potential," Tullow's Exploration Director Angus McCoss said in a statement.

In March, the company said some of its oil reserve areas in Kenya were poorly developed, though it remained upbeat about their potential.

Its partners at Africa Oil Corp. said testing last year from the reserves areas in blocks 10BB and 13T in northern Kenya yielded a flow rate of about 5,000 barrels of oil per day.

In a separate statement Wednesday, Africa Oil Chief Executive Officer Keith Hill said his company was "very bullish" about its opportunities in Kenya.

"Our goal is to open up at least one new basin and to move a significant number of barrels from prospective to contingent resources by the end of 2014 as we move the field development program forward," he said.