Timeline: Gulf of Mexico oil spill

HOUSTON (Reuters) - Here is a timeline on the Gulf of Mexico oil spill and its impact since an explosion on a rig killed 11 workers. It is the worst accidental offshore oil spill in history.

* April 20, 2010 - Explosion and fire on Transocean Ltd’s drilling rig Deepwater Horizon licensed to BP Plc, killing 11 workers. The rig was drilling in BP’s Macondo project 42 miles southeast of Venice, Louisiana, in 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 (8-km) oil slick forms.

* April 25 - The U.S. Coast Guard says underwater cameras detect a leak of 1,000 barrels of oil per day. Underwater robots try to shut valves on the blowout preventer to stop the leak, but BP abandons that failed effort two weeks later.

* 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 until the cause of the accident is known, wiping out widened access granted three weeks before the disaster.

* - 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 near the failed well.

* May 7 - An attempt to place a steel 98-ton containment dome over the spewing well fails to contain the oil.

* 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 in his sternest comments yet.

* May 19 - The first 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 27 - U.S. scientists estimate the leak has spewed 12,000 to 19,000 barrels of oil per day, much higher than previous government estimates of 5,000 barrels per day, and more than four times the amount the Exxon Valdez spilled into Alaska’s Prince William Sound in 1989.

* May 28 - The Obama Administration imposes a six-month ban on new deepwater drilling.

* May 29 - BP says the complex “top kill” maneuver, started three days earlier by pumping heavy drilling mud into the well to smother the leak, failed to hold back gushing oil.

* June 1 - BP shares plunge 17 percent in London trading, wiping $23 billion off its market value, on news of the top kill failure.

-- 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 - U.S. authorities expand fishing restrictions to cover 37 percent of U.S. federal waters in the Gulf.

* June 3 - Underwater robots saw off a bent pipe from the top of blowout preventer equipment to make way for a cap on the wellhead.

* Several drilling companies sue the Obama Administration to challenge the deepwater drilling moratorium.

* June 8 - Obama says he wants to know “whose ass to kick” over the spill, adding to the pressure on BP.

* 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 - In first comments, British Prime Minister David Cameron says Britain is ready to help BP deal with the spill.

-- U.S. scientists double high-end estimate of the leak’s flow rate through June 3, when robots sawed off the bent pipe, to between 20,000 and 40,000 barrels (840,000 and 1.7 million gallons/3.2 million and 6.4 million liters) of oil per day.

* June 11 - Supportive comments from Britain lift BP’s shares in London by 6.4 percent, but not enough to restore the company’s worth to pre-spill levels. BP is worth 70 billion pounds ($102 billion) against more than 120 billion pounds in April.

* June 14 - Two U.S. lawmakers release a letter to 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 - CEOs of Exxon Mobil, Chevron, ConocoPhillips and the U.S. arms of Royal Dutch Shell tell lawmakers at a congressional hearing that their offshore operations are safe and their companies would not have designed a deepwater well the way BP designed Macondo.

* June 16 - Hayward and BP Chairman Carl-Henric Svanberg meet with White House officials and announce an agreement to set up a $20 billion fund for damage claims from the spill. BP also suspends dividend payments to shareholders and says it will pay $100 million to workers idled by the six-month moratorium on deep-sea drilling.

* June 17 - Hayward appears before a congressional hearing. He apologizes for the spill and says everything is being done to stop it. Lawmakers accuse BP of cutting corners to boost profits.

* June 18 - Anadarko Petroleum, part owner of the gushing well, says BP was “reckless” and likely represented “gross negligence or willful misconduct,” which would affect obligations of the well owners.