Listed exploration company Tullow Oil has assigned a 42.5 per cent interest in one of its drilling licences in Africa to Addax Petroleum.

In a statement yesterday, Tullow said it would continue as operator of the offshore Kiarsseny Martin Licence, which it took over last year in Gabon, as well as retain a 57.5 per cent interest. But Addax will take the remaining interest, while bearing the drilling costs of the Kiarsseny Topaze South well.

Tullow said drilling of the well would begin later this month. In the event of success, the farm-out agreement - subject to approval by the Gabon government - provides for Addax to bear the drilling costs of up to two additional exploration and appraisal wells on the same licence.

Addax, which was founded in 1994 to exploit oil and gas fields in West Africa, has already worked in partnership with Tullow in Cameroon.

Mr Aidan Heavey, chief executive of Tullow, said its West African assets were "at the core" of its international growth strategy and the company would continue to seek opportunities in the region. "The Topaze well is part of an active exploration programme for the first half of 2004 covering all of Tullow's core areas, with other wells also drilling or imminent in Bangladesh and the UK," he said.

Davy analyst Mr Job Langbroek said yesterday that the catalyst for Tullow moving off the trading range it had been in over the past year would be "crystalising value" from one of its exploration projects.