(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 the huge spill.
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 5-mile-long oil slick forms.
April 25 - Efforts to activate the well's blowout preventer fail.
April 29 - U.S. President Barack Obama pledges "every single available resource," including the U.S. military, to contain the spreading spill and says BP is responsible for the cleanup.
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 and will pay all legitimate claims and the cost of the cleanup.
May 2 - Obama visits the Gulf Coast. U.S. officials close areas affected by the spill to fishing for 10 days. BP starts drilling a relief well alongside the failed well, a process that may take two to three months to complete.
May 7 - An attempt to place a containment dome over the spewing well fails when the device is rendered useless by frozen hydrocarbons that clogged it.
May 9 - BP says it might try to plug the undersea leak by pumping materials such as shredded 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. 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 inserts a tube into the leaking riser pile of the well and captures some oil and gas.
May 19 - The first heavy oil from the spill hits fragile Louisiana marshlands. Part of the slick enters a powerful current that could carry it to the Florida Keys and beyond.
May 26 - A "top kill" maneuver starts, involving pumping drilling mud and other material into the well shaft to try to stifle the flow.
May 28 - Obama tours the Louisiana coast, saying, "I am the president and the buck stops with me."
-- BP CEO Tony Hayward flies over the Gulf.
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 on 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 tries another capping strategy but has difficulty cutting off a leaking riser pipe.
-- U.S. authorities expand fishing restrictions to cover 37 percent of U.S. federal waters in the Gulf.
June 4 - Obama, on his third trip to the region, warns BP against skimping on compensation to residents and businesses.
June 7 - BP, which says it has now spent $1.25 billion on the spill, sees shares gain on news of the progress in containing the leak.
June 8 - Obama says he wants to know "whose ass to kick" over the spill, adding to the pressure on BP.
-- U.S. weather forecasters give their first confirmation that some of the oil leaking has lingered beneath the surface rather than rising to the top.
June 9 - U.S. Interior Secretary Ken Salazar says BP must pay the salaries of thousands of workers laid off by a moratorium on drilling, at a congressional hearing.
June 10 - The White House says that Obama has invited BP Chairman Carl-Henric Svanberg to the White House on June 16 to discuss the spill.
-- In his first comments, Prime Minister David Cameron says Britain is ready to help BP deal with the spill.
-- U.S. scientists double their estimates of the amount of oil gushing from the well, saying between 20,000 and 40,000 barrels (840,000 and 1.7 million gallons/3.2 million and 6.4 million liters) of oil flowed from the well before June 3.
June 11 - Supportive comments from Britain lift BP's shares in London gaining 6.4 percent. However the rise does not mend damage done to BP shares -- the company is worth 70 billion pounds ($102 billion) against over 120 billion pounds in April.
June 14 - Obama, on his fourth trip to the Gulf, says he will press BP executives at a White House meeting on June 16 to deal "justly, fairly and promptly" with damage claims.
-- Under intense pressure, BP unveils a new plan to vastly boost the amount of oil it is siphoning off.
-- Two U.S. lawmakers release a letter to BP CEO Hayward saying: "It appears that BP repeatedly chose risky procedures in order to reduce costs and save time and made minimal efforts to contain the added risk."
June 15 - Lawmakers summon top executives from Exxon Mobil, Chevron, ConocoPhillips and Royal Dutch Shell and BP -- in what is likely to be a heated showdown on the safety of drilling in the deep waters off America's coasts.
-- Obama said in his first televised speech from the Oval Office in the White House: "But make no mistake: we will fight this spill with everything we've got for as long it takes. We will make BP pay for the damage their company has caused. And we will do whatever's necessary to help the Gulf Coast and its people recover from this tragedy."
(Writing by David Cutler, London Editorial Reference Unit)