Ten bodies have been found during a rescue operation off the coast of Nigeria after a tugboat contracted by Chevron sank on Sunday in rough seas, the vessel's owner said on Friday.
The Jascon-4 capsized early on Sunday at a mooring point around 30 km (20 miles) off oil-producing Delta state. Of 12 people who had been on board, one was rescued alive and another is still missing.
"The search and rescue operation that has been under way since 26 May has had to be stopped for safety reasons," the ship's owner West African Ventures said in a statement.
"The vessel, which is located some 30 metres under water in an upside-down position, has become so unstable that the risk of injury to our rescue divers has become unacceptably high," said West African Ventures, which is owned by Sea Trucks Group.
Chevron operates offshore and onshore joint ventures with the Nigerian National Petroleum Corp and says it spends around $3 billion a year on its Nigerian operations.
The U.S. energy firm's 2012 net daily production from Nigeria was 238,000 barrels of crude oil, 165 million cubic feet of natural gas and 4,000 barrels of liquefied petroleum gas.