Millions of gallons (liters) of oil have poured into the Gulf of Mexico since an April 20 blast on the Deepwater Horizon rig triggered a huge spill, soiling 100 miles of coastline, threatening some of the United States' richest fisheries and endangering a fragile ecosystem.
Below is a timeline of the spill and its impact:
April 20, 2010 - Explosion and fire on Transocean Ltd's drilling rig Deepwater Horizon licensed to BP; 11 workers are killed. The rig was drilling in BP's Macondo project 42 miles southeast of Venice, Louisiana, beneath about 5,000 feet of water and 13,000 feet under the seabed.
April 22 - The Deepwater Horizon rig, valued at more than $560 million, sinks and a five mile long oil slick is seen.
April 25 - The Coast Guard says remote underwater cameras detect the well is leaking 1,000 barrels of crude oil per day. It approves a plan to have remote underwater vehicles activate a blowout preventer and stop leak. Efforts to activate the blowout preventer fail.
April 28 - The Coast Guard says the flow of oil is 5,000 barrels per day (bpd) (210,000 gallons/795,000 liters) -- five times greater than first estimated. A controlled burn is held on the giant oil slick.
April 29 - Obama pledges "every single available resource," including the U.S. military, to contain the spreading spill.
-- Obama also says BP is responsible for the cleanup. Louisiana declares state of emergency due to the threat to the state's natural resources.
April 30 - An Obama aide says no drilling will be allowed in new areas, as the president had recently proposed, until the cause of the Deepwater Horizon accident is known.
-- BP Chairman Tony Hayward says the company takes full responsibility for the spill and would pay all legitimate claims and the cost of the cleanup.
May 2 - Obama visits the Gulf Coast to see cleanup efforts first hand. U.S. officials close areas affected by the spill to fishing for an initial period of 10 days. BP starts to drill a relief well alongside the failed well, a process that could take two to three months to complete.
May 5 - A barge begins towing a 98-ton containment chamber to the site of the leak. BP says one of the three leaks has been shut off by capping a valve, but that would not cut the amount of oil gushing out.
May 6 - Oil washes ashore on the Chandeleur Islands off the Louisiana coast, uninhabited barrier islands that are part of the Breton National Wildlife Refuge.
May 7 - BP tries 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. -- A fishing ban for federal waters off the Gulf is modified, expanded and extended to May 17.
May 9 - BP says it might try to plug the undersea leak by pumping materials such as shredded up tires and golf balls into the well at high pressure, a method called a "junk shot."
May 11/12 - Executives from BP, Transocean and Halliburton appear at congressional hearings in Washington. Senate Energy committee chairman Jeff Bingaman says that it appeared that the explosion on the rig was due to a "cascade of errors, technical, human and regulatory. The executives blame each other's companies.
May 14 - Obama slams companies involved in the spill, criticizing them for a "ridiculous spectacle" of publicly trading blame over the accident in his sternest comments yet.
May 16 - BP succeeds in inserting a tube into the leaking well and capturing some oil and gas.
May 18 - The U.S. nearly doubles a no-fishing zone in waters affected by the oil, extending it to 19 percent of U.S. waters in the Gulf.
May 19 - The first heavy oil from the spill sloshes ashore in fragile Louisiana marshlands and part of the mess enters a powerful current that could carry it to Florida and beyond.
May 26 - A "top kill" maneuver starts involving pumping heavy fluids and other material into the well shaft to stifle the flow, then sealing it with cement.
May 28 - Obama tours the Louisiana Gulf coast on his second visit - "I am the president and the buck stops with me," he said.
-- BP CEO Tony Hayward flies over the Gulf. BP says that the cost of the disaster so far is $930 million. May 29 - BP says the complex "top kill" maneuver to plug the well has failed, crushing hopes for a quick end to the largest oil spill in U.S. history already in its 40th day.
May 31 - The U.S. government and BP are warning that the blown-out oil well may not be stopped until August as the company prepares a new attempt to capture leaking crude.
June 1 - BP shares plunge 17 percent in London trading, wiping $23 billion off its market value, on news its latest attempt to plug the well has failed.
(Reporting by Erwin Seba and Ros Krasny: Additional writing and editing by David Cutler, London Editorial Reference Unit)