The well, 5,000 feet 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.

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 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.

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 liters) of oil into the Prince William Sound in Alaska when it ran aground in 1989. The well, which is owned by BP, is spewing about 42,000 gallons (190,900 liters) of oil a day into the ocean, the Coast Guard estimates.