Exxon’s acquisition of 23.49 percent of the Jubilee oil field underscored the interest that energy companies have shown in the 700 miles of Western African coastline that stretches from Sierra Leone to Ghana. Last month, the Italian oil giant Eni agreed to buy two fields off Ghana from the Vitol Group, a major oil-trading firm.
The Jubilee stake, which was owned by Kosmos Energy, a company based in Dallas and backed by major private equity firms, had attracted several companies and had started a bidding war between international and state-owned players, including Chinese companies.
But in a letter sent to the other bidders on Monday, Kosmos said it had “entered into a binding agreement with an exclusive bidder,” said the person, who declined to be identified because the negotiations were private.
Because of higher oil prices since the beginning of the decade, companies have increased their spending on exploration. While major companies like Exxon have focused on developing large oil and gas projects, much of the riskier and more prospective exploration has been undertaken by smaller, independent producers like Anadarko Petroleum, Tullow Oil and Kosmos.
Last month, for example, Anadarko announced that it had made a major discovery after drilling the first deepwater well off the coast of Sierra Leone. The company, along with Tullow Oil, owns the rest of the Jubilee field.
Fadel Gheit, an analyst at Oppenheimer & Company, said that Exxon was paying a steep price for the reserves at a time when oil companies were struggling to gain access to resources in traditional regions, like Russia or Venezuela. Exxon needs to find 1.5 billion barrels of reserves each year to replace the oil and gas it pumps annually.
“The world is getting smaller in terms of access,” Mr. Gheit said. “And Exxon has to run harder just to stay in place.”
A representative from Kosmos did not return calls or respond to e-mail messages seeking comment. Exxon also declined to comment about its bid.
“Exxon Mobil routinely evaluates potential development opportunities around the world,” Patrick McGinn, a spokesman for Exxon, said.
Kosmos, along with Anadarko and Tullow, have been particularly successful in Ghana where they have found oil in all of the eight wells they drilled in recent years. The partners have found four major fields — Jubilee, Odum, Tweneboa and Mahogany — and have identified four more potential prospects.
Jubilee, which was discovered in 2007, should start producing oil by the end of next year, and is expected to eventually pump about 120,000 barrels a day. Kosmos has estimated that Jubilee could hold recoverable oil and gas reserves of as much as two billion barrels. That puts the field in the same class of discoveries that have been recorded in the Gulf of Mexico in recent years.
The purchase also guarantees a big payday for the private equity companies that own Kosmos — Warburg Pincus, with 55 percent, and the Blackstone Group, with 45 percent. Since 2004, Blackstone and Warburg have invested $1.1 billion in Kosmos.
The acquisition still requires approval from the government of Ghana.