Chevron said it was still investigating the fire, which occurred near its North Apoi oil platform, and which forced it to shut down.
"We immediately flew out people to the nearby North Apoi platform, and have been helping those needing any medical assistance," Chevron spokesman Scott Walker said in a statement.
Chevron did not immediately say what caused the fire. However, Nigeria's government believes a "gas kick" — a major build up of gas pressure from drilling — was responsible, said Levi Ajuonoma, a spokesman for the state-run Nigerian National Petroleum Corp.
Chevron and other foreign oil companies in Nigeria pump crude oil in partnership with the state-run company.
Nnimmo Bassey, who runs an environmental watchdog group in Nigeria, said he had received reports from locals nearby that the fire was an industrial incident.
"Workers were trying to contain the gas pressure and they didn't succeed," Bassey said.
The rig is run on Chevron's behalf by contractor FODE Drilling Co., Walker said. Officials with FODE, which has offices in London and Jenkintown, Pennsylvania, could not be immediately reached for comment Monday.
Nigeria is the fifth-largest crude oil exporter to the U.S. It produces about 2.4 million barrels of crude oil a day. However, more than 50 years of oil production has seen environmental damage through delta's maze of muddy creeks and mangroves.
Chevron, based in San Ramon, California, produced an average of 524,000 barrels of crude oil a day from Nigeria in 2010. The company has exploration rights to about 2.2 million acres across Nigeria's delta and offshore.Suggest a correction