Exxon Mobil (XOM: 71.2426, 0.9626, 1.37%) signed an exclusive deal with Ghanan oil company Kosmos Energy on Monday that will give the American oil giant access to a large oil field off the coast of Ghana, according to a report by The Wall Street Journal.

The deal comes after earlier reports that Kosmos Energy was in advanced talks with Chinese oil drilling company China National Offshore Oil Corp., commonly known as Cnooc (CEO: 154.89, 5.93, 3.98%).

"I can confirm that Kosmos has entered into an exclusive binding agreement with a third party (an affiliate of Exxon Mobil) in relation to the sale of its Ghana assets," Kosmos Senior Vice President and Chief Financial Officer Greg Dunlevy said in an e-mail to The Wall Street Journal.

The deal, worth an estimated $4 billion, would give Exxon access to the Ghanaian "Julibee" oil field with an estimated 1.8 billion barrels of oil equivalent - most of it the high-quality sweet oil that Western European and American businesses and consumers need.

The deal is not final, according to the Journal, and would still need the approval of the Ghanaian government, who have the right to cancel the contract at any time.

The deal could be a major economic boon for the country of Ghana, which has recently moved into the world stage as a large holder of oil.