| HOUSTON/GALLIANO, Louisiana
HOUSTON/GALLIANO, Louisiana Energy giant BP marked a limited success at containing the oil that is gushing unabated into the Gulf of Mexico on Sunday and said it may be able to stop the flow permanently in about a week.
But reports of huge oil plumes in the Gulf -- including one as large as 10 miles long, three miles wide and 300 feet thick -- underscored the spill's environmental impact as the crisis moved into its 24th day.
Crude oil has been gushing unchecked from a ruptured well about a mile under the ocean's surface, threatening an ecological and economic calamity along the U.S. Gulf Coast.
After other attempts to contain the spill failed, BP Plc succeeded in inserting a tube into the leaking well and capturing some oil and gas.
The underwater operation used guided robots to insert a small tube into a 21-inch (53-cm) pipe, known as a riser, to funnel the oil to a ship at the surface.
"It's working as planned and we are very slowly increasing the rate that is coming from the riser tool up to the surface," BP senior executive vice president Kent Wells told reporters at BP's U.S. headquarters in Houston. "So we do have oil and gas coming to the ship now."
Not all of the oil was being trapped, however. Wells said it was too early to say how much had been siphoned.
"This is a good step forward," said Satish Nagarajaiah, professor in civil and mechanical engineering at Rice University in Houston, but he said the siphon tool is unlikely to capture more than 15-20 percent of the oil.
"NOT A SOLUTION"
The Obama administration downplayed the significance of BP's latest breakthrough.
"This technique is not a solution to the problem, and it is not yet clear how successful it may be," Secretary of Homeland Security Janet Napolitano and Secretary of the Interior Ken Salazar said in a joint statement.
Preparations for a maneuver to inject mud into the well to stop the leak for good were ongoing and would be completed in seven to 10 days, Wells said. Undersea robots are preparing pipes and hoses around the well to pump up to 40 barrels (1,680 gallons) per minute of mud into the well.
BP's best near-term hope of stopping oil from pouring from the well is "kill mud," a heavy mixture of synthetic materials that technicians will attempt to shoot into the well to form a barrier to prevent oil and gas from escaping.
"Ultimately it is a winning game that we outpump the well," Wells said.
If the mud fails to seal the well, BP will attempt to inject golf balls, tire fragments and other materials into the well to clog it up, known in the industry as a "junk shot."
The success on Sunday followed a previous setback, when a cord taking the oil to the surface became entangled.
BP's earlier attempts to contain the leaking well have been stymied by the technical difficulties of working in the sea floor's cold, dark conditions.
On May 7, BP tried to lower a containment dome over the leak, but the 100-tonne device was rendered useless by a slush of frozen hydrocarbons that clogged it.
The spill began after an April 20 explosion on the Deepwater Horizon rig that killed 11 workers. It threatens to eclipse the 1989 Exxon Valdez spill off Alaska as the worst U.S. ecological disaster.
POTENTIAL RISK TO THE EAST, FLORIDA KEYS
So far, winds have pushed the giant slick westward and toward shore.
But according to the National Oceanic and Atmospheric Administration, the southern edge of the spill could make its way into a powerful ocean current that could carry oil eastward toward the Florida Keys and up the U.S. Eastern Seaboard.
"The southern edge of the plume could begin moving more to the southwest and potentially into the Loop Current," NOAA said on its website, referring to the deep ocean stream that transfers heat from the tropics to higher latitudes and becomes the Gulf Stream.
Officials have stressed the spill has had minimal impact on the shoreline and wildlife, but oil debris and tar balls were washing up on barrier islands and outlying beaches in at least a dozen places in Louisiana, Alabama and Mississippi.
"As nasty as they are, they are more manageable than a slick. They can be collected. They can be cleaned and we have crews doing that," said Coast Guard Petty Officer Luke Pinneo, referring to the tar balls found on Grand Isle, Louisiana.
Scientists and residents of the Gulf Coast say a greater concern is the anticipated encroachment of oil into the environmentally fragile bayous and marshes teeming with shrimp, oysters, crabs, fish, birds and other wildlife.
The New York Times and other media reported scientists had detected huge oil plumes -- large columns of concentrated oil moving beneath the ocean surface -- in the Gulf, indicating the leak could be worse than estimates by BP and the government.
Estimates of the rate of escaping oil range widely from the official BP figure of 5,000 barrels per day (210,000 gallons/795,000 liters), adopted by the government, to 100,000 barrels (4.2 million gallons/15.9 million liters) per day.
BP said it had no confirmation of such undersea oil plumes and its spokesman, Andrew Gowers, appeared to dismiss the reports as scientifically unlikely.
"It is my observation as a layman that oil is lighter than water and tends to go up," Gowers told reporters.
BP is facing growing political pressure to prove it will pay for all of the costs related to the spill.
Salazar and Napolitano demanded in a letter to BP Chief Executive Tony Hayward that the company make clear its commitment to "redress all of the damage that has occurred or that will occur in the future as a result of the oil spill."
The letter was released on Saturday and amid concerns about the implications of a U.S. law that limits energy companies' liability for lost business and local tax revenues from oil spills to $75 million.
BP spokesman David Nicholas said: "What they are requesting in the letter is absolutely consistent with all our public statements on the matter.
President Barack Obama's administration wants to raise the liability limit retroactively.
(Additional reporting by Jeff Mason, Matthew Bigg, and Tom Bergin; Writing by Jeff Mason; Editing by Ed Stoddard and Chris Wilson)