British oil major BP is now changing tack. After the four-story dome failed against the relentlessly spreading oil spill in the Gulf of Mexico, it is now trying to put in place a pipe ringed with a gasket to seal the undersea well and channel the oil to a ship.
If the new plan fails, BP could try using a smaller containment dome -- dubbed a "top hat" -- that would be injected with alcohol to act as an antifreeze and keep its outlet clear. And still under consideration is a proposal to plug the damaged well's blowout preventer, which has failed to cut off the leak, with debris such as ground-up rubber and plastic from old tires and golf balls.
The debris would be injected at high pressure into the blowout preventer, a 450-ton device that sits atop the wellhead. If that succeeds, the well would be injected with cement to seal it.
The drill rig Deepwater Horizon exploded April 20 and sank two days later, about 50 miles off the southeast coast of Louisiana, leaving 11 workers lost at sea. The well has been pouring an estimated 210,000 gallons (5,000 barrels) of light, sweet crude into the Gulf for three weeks now. But so far, natural forces, human effort and some good fortune have kept the spill from becoming all-out environmental disaster, scientists said.
BP, the Coast Guard, and state and local authorities have scrambled to keep the oil from reaching shore or the ecologically delicate coastal wetlands off Louisiana. They have burned off patches of the slick, deployed more than 280 miles of protective booms, skimmed as much as 4 million gallons of oily water off the surface of the Gulf and pumped more than 400,000 gallons of chemical dispersants onto the oil.
Nevertheless, oil has washed up on barrier islands in Louisiana's Breton and Chandeleur sounds, spread west of the Mississippi River, and balls of tar associated with the spill have been reported as far east as Dauphin Island, off the Alabama coast. And the federal government has closed the area to commercial fishing, curtailing one of the region's biggest industries.
An oily sheen has reached the shores of some of Louisiana's barrier islands, but there has been no repeat of disastrous scenes of widespread oil-soaked wildlife and beaches, as in the 1989 wreck of the supertanker Exxon Valdez in Alaska's Prince William Sound.
"One of the things that's been happening is, the weather has worked in our favor so far," said Steven Lohrenz, marine science chairman at the University of Southern Mississippi. Ocean currents and prevailing winds have carried much of the spilled oil away from the coast, although the wind has changed in the past week, he said.
"The currents are very complex in that area, and they change pretty dramatically, so it's very difficult to predict what they will do," he said.
Meantime BP has also come in for criticism over the type of dispersants it is using.
After the Deepwater Horizon explosion, BP quickly marshaled a third of the world's available supply of dispersants, chemicals that break surface oil slicks into microscopic droplets that can sink into the sea.
But the benefits of keeping some oil out of beaches and wetlands carry uncertain costs. Scientists warn that the dispersed oil, as well as the dispersants themselves, might cause long-term harm to marine life.
The company continues to stockpile and deploy oil-dispersing chemicals manufactured by a company with which it shares close ties, even though other U.S. EPA-approved alternatives have been shown to be far less toxic and, in some cases, nearly twice as effective, wrote Paul Quinlan in New York Times.