Anadarko, the US oil group, and its partners Woodside of Australia, Repsol of Spain and Tullow Oil of the UK, yesterday confirmed they had found a new offshore oil region from Sierra Leone to Ghana in which they expect to discover more huge oil fields in the next five years.

The announcement was made based on positive drilling results from the Venus well off the coast of Sierra Leone, 1,100km from Ghana's Jubilee field, Africa's largest deep-water field.

“The chance of there being at least one more Jubilee-sized field along the coast between Ghana and Sierra Leone has greatly increased,” said Aidan Heavey, Tullow chief executive.

The Jubilee field, discovered in 2007, holds up to 2bn barrels of oil. It will propel Ghana into the world's top 50 producers after it begins to produce next year and has helped to more than triple Tullow's market capitalisation.

Shares in Anadarko, which has 40 per cent of Venus, Tullow, with 10 per cent, and Woodside and Repsol, each with 25 per cent, all rose in response to the Venus discovery.

The results of drilling, which has been one of the most closely watched in the industry, itself suggests a large field. But much more important is the area it opens up.

Bob Daniels, head of Anadarko exploration, said: “The Venus discovery confirms the existence of an active petroleum system in the basin and enhances the prospectivity of our vast West Africa acreage.”

Bob MacKnight, analyst at consultant PFC Energy, said the area was the first “truly new” deep water oil region to open up in more than a decade.