Reporting from Port Fourchon, La. — As the odds of survival for 11 missing workers diminished Thursday, officials warned that the dramatic explosion and fire that sank an oil rig off the Louisiana coast may pose a serious environmental threat if oil is leaking thousands of feet below the surface.
"It certainly has the potential to be a major spill," said Dave Rainey, vice president of Gulf of Mexico exploration for the oil company BP, which leased the Deepwater Horizon, the $600-million mobile offshore rig that vanished underwater Thursday morning.
Throughout the day, rescue aircraft and Coast Guard cutters scoured the gulf for signs of the workers who were missing after the Tuesday evening explosion. Coast Guard Rear Adm. Mary E. Landry said that the probability of their survival was decreasing, despite warm waters and calm seas.
Landry also said that preliminary interviews with some of the 115 survivors suggested that some of the missing workers "may have been in the vicinity of the explosion."
Adrian Rose, vice president of Transocean Ltd., the rig's owner, said survivors told them the missing workers might not have been able to evacuate.
"We haven't confirmed that yet, and search and rescue efforts are continuing," he said. "I know that everyone at Transocean shares a deep sense of loss today, especially the crew members of the Deepwater Horizon who work and live together as a family on board the rig offshore."
Beyond the immediate human drama, numerous questions remained unanswered. The cause of the explosion remains unclear, although Rose and government officials have speculated that it was the result of a "blowout," or high-pressure surge of oil or natural gas.
Also pressing were the mysteries 5,000 feet below the sea, where a remote-controlled submarine was trying to ascertain whether oil or gas was flowing out of the well.
In a Thursday afternoon news conference, Coast Guard and oil company officials said it was not clear whether the 18,000-foot-deep well was still leaking.
Earlier in the day, Coast Guard firefighter Katherine McNamara said the rig had been spurting crude oil at a rate of 336,000 gallons per day, though nearly all of it was burning off in the incessant fire.
In the afternoon, after the rig sank, Landry said that it was not yet possible to know how much oil and gas, if any, was seeping from the well head.
Another possible environmental threat was the 700,000 gallons of diesel oil stored in the rig. Explosions and fires continued on the rig until it sank at about 10:22 a.m. Thursday. Landry said it was unclear how much, if any, of the diesel had leaked or blown up.
Two underwater pipelines near the rig have been shut down for fear that they might be hit by the sinking oil rig, which is longer than a football field.
A 1-by-5-mile sheen of a crude oil mixture has appeared on the water's surface near the site, which is roughly 40-plus miles southeast of Venice, La. Landry said it was "probably residual" oil and other substances from the explosion and fire.
Thus far, there has been no impact to the fragile Louisiana coastline, officials said, Deputy Interior Secretary David J. Hayes, who also spoke from New Orleans, said the government was watching the slick carefully.
The Coast Guard had already positioned special ships to skim the oil and were preparing to send planes to spray dispersants. These, typically, are solvents and other agents that change the chemical and physical properties of oil and may reduce the threat to the shoreline.
Rigs like the Deepwater Horizon are not moored to the ocean bottom, nor do they pump out oil. They float over a location, holding their position with GPS systems and propellers, and drill wells for future oil production.
Introduced to the seas in 2001, the Deepwater Horizon was on the cutting edge of the offshore industry. It was capable of operating in more than 8,000 feet of water, according to the company's website, and last summer it set a record for drilling the world's deepest oil and gas well of more than 35,000 feet at another site in the gulf.
Just before the explosion, the rig's crew was preparing to plug the well and abandon it, leaving it ready for later extraction efforts.
Rose said Thursday the fact that the rig drilled to such extreme depths, and in such deep water, did not increase the possibility of danger or an accident.
Three people were hospitalized with critical injuries. But the bulk of the workers — more than 90 — arrived safely on shore at Port Fourchon early Thursday, and were taken to a hotel near the New Orleans airport.
After sunrise, rig workers were milling, somewhat dazed, around the hotel lobby. Some were still dressed in the orange or slate-gray jumpsuits they wear on the job. Some were surrounded by relieved family and friends.
At one point, a burly worker on crutches with a bandaged leg faltered on his walk toward a breakfast room. A tight scrum of family members caught him and held him up.