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June 3 (Reuters) - 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 (160 km) of coastline, threatening some of the richest U.S. fisheries and endangering a fragile marine 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 (BP.L); 11 workers are killed. The rig was drilling in BP's Macondo project 42 miles (68 km) southeast of Venice, Louisiana, beneath about 5,000 feet (1,525 metres) of water and 13,000 feet (4 km) under the seabed.
April 22 - The Deepwater Horizon rig, valued at more than $560 million, sinks and a five mile long (8 km) oil slick is seen.
April 25 - The Coast Guard 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 litres) -- five times greater than first estimated. A controlled burn is held on the giant oil slick.
April 29 - U.S. President Barack 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 Chief Executive 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 will 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 will 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 the containment dome over the leak, but the 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.
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 appears that the explosion on the rig is 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 riser pile of the 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 fragmented oil slick enters a powerful current that could carry it to the Florida Keys and beyond.
May 26 - A "top kill" maneuver starts, involving pumping heavy fluids and other material into the well shaft to try to stifle the flow.
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 the disaster has so far cost the company $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.
June 1 - BP shares plunge 17 percent in London trading, wiping $23 billion off its market value, on news the latest attempt to plug the well has failed.
-- U.S. Attorney General Eric Holder says the Justice Department has launched a criminal and civil investigation into the rig explosion and the spill.
June 2 - BP continues work on a new plan to try to capture most of the escaping oil. This involves using robot submarines to cut off what is left of the leaking riser pipe, then lowering a containment cap over the wellhead assembly. Some difficulties are encountered with the cutting operation.
-- U.S. authorities expand fishing restrictions to cover 37 percent of U.S. federal waters in the Gulf.
June 3 - After previous sharp declines, BP shares rise more than 3 percent on market hopes that the latest plan to control the leaking well may make some progress. The six-week-old crisis has wiped a third off BP's market value since it began. (Compiled by David Cutler, London Editorial Reference Unit; Editing by Pascal Fletcher)