U.S. agencies on Sunday approved a plan to use remote-controlled underwater vehicles to seal a leaking oil well beneath a drilling rig that exploded and sank in the Gulf of Mexico last week.
The well, 5,000 feet (1,525 metres) under the ocean surface off Louisiana's coast, is leaking about 1,000 barrels of oil a day. The spill, which the U.S. Coast Guard has called "very serious," could threaten the Gulf Coast's fragile ecosystem if not contained.
Four underwater vehicles have been deployed under the plan outlined by the Coast Guard and U.S. Minerals Management Service. They will dive unmanned to the ocean floor to activate a blowout preventer, a giant series of pipes and valves that could staunch the leak.
Swiss-based Transocean Ltd's Deepwater Horizon sank on Thursday, two days after it exploded and caught fire while finishing a well for BP Plc 42 miles (68 km) off the Louisiana coast.
Eleven workers from the rig are missing and presumed dead in what is the worst oil rig disaster in almost a decade. The Coast Guard on Friday suspended a search for the workers.
London-based BP, which is financially responsible for the cleanup, has deployed an armada of ships and aircraft to contain the oil slick.
Weather models predict it will remain about 30 miles (48 km) off shore for the next three days, said Coast Guard Rear Admiral Mary Landry. "We have no shoreline impacts at this time," Landry told reporters at a briefing. The oily sheen covered about 400 square miles (1,036 sq km) as of Saturday.
Activating the blowout preventer is a "highly complex task" and "it may not be successful," said Doug Suttles, chief operating officer of BP's exploration and production unit.
The blowout preventer -- which weighs about 450 tons and sits on the sea floor next to the well -- could take 24-36 hours to activate, Suttles said.
As a backup, BP is sending two floating drilling rigs to the scene that could drill a series of relief wells to stop the leak. That operation, if needed, could take months, Suttles said.
The spill currently is not comparable with the infamous Exxon Valdez disaster, which spilled about 11 million gallons (50 million litres) of oil into the Prince William Sound in Alaska when it ran aground in 1989. The Transocean well is spewing about 42,000 gallons (190,900 litres) of oil a day into the ocean, the Coast Guard estimates.
The explosion came almost three weeks after President Barack Obama unveiled plans for a limited expansion of U.S. offshore oil and gas drilling. It has not affected U.S. oil markets.
The explosion occurred as the rig was capping a discovery well pending production, company officials said. Some 115 of the 126 workers on board at the time of the explosion were rescued.