The estimate assumes Cnooc will pay a 10 percent premium over the value it paid earlier this year for 20 percent of Pan American because the BP stake would give it control of the company, Citigroup analysts Graham Cunningham and Tushar Bagla said in a report yesterday.

BP needs to complete the sale of as much as $30 billion of assets over the next 18 months to start making compensation payments for the largest oil spill in U.S. history earlier this year. Occidental Petroleum Corp., Total SA and Apache Corp. are among companies operating in Argentina that may be interested in partnering with Cnooc to buy the stake in the country’s largest oil exporter, the analysts said.

Chinese oil companies are seeking assets overseas to secure crude supplies for the world’s fastest-growing major economy. China Petrochemical Corp., known as Sinopec Group, bought Addax Petroleum Corp. for C$8.3 billion ($8 billion) last year to add oil reserves, part of the record $32 billion of acquisitions by Chinese companies in natural resources.

Cnooc bought 20 percent of Pan American in March through the acquisition of a 50 percent stake in Bridas Corp. for $3.1 billion from Argentina’s Bulgheroni family.

OGX Bid

Cnooc and Sinopec may offer at least $7 billion for assets of Brazil’s OGX Petroleo & Gas Participacoes SA, two people with knowledge of the matter said last week. Brazilian billionaire Eike Batista, who controls OGX, confirmed on Sept. 13 the Chinese companies are among bidders for the assets. The Rio de Janeiro-based company plans to sell a stake of as much as 30 percent in oil fields in Brazil’s Campos Basin.

Pan American Energy is Argentina’s largest exporter of crude and the second largest producer, behind Repsol YPF SA, with about 17 percent of the country’s overall crude output.