TIMELINE-Gulf of Mexico oil spill

July 15 (Reuters) - Millions of gallons/liters of oil have
spewed into the Gulf of Mexico since an April 20 explosion on a
drilling rig triggered the worst spill in U.S. history.

Below is a timeline of the disaster and its impact.

April 20, 2010 - Explosion and fire on Transocean Ltd's
drilling rig Deepwater Horizon licensed to BP Plc (BP.L)
BP.N.; 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 5-mile (8 km) 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
clean-up.

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 clean-up.

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 11/12 - Executives from BP, Transocean (RIG.N) and
Halliburton (HAL.N) 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 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 28 - Obama tours the Louisiana coast, saying "I am the
president and the buck stops with me."

-- Hayward flies over the Gulf.

May 29 - BP says the complex "top kill" maneuver, started
three days earlier to plug the well, has failed.

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 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 - 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 litres) flowed out before June 3.

June 11 - Supportive comments from Britain lift BP's shares
in London by 6.4 percent. But the rise does not mend the damage
done -- the company is worth 70 billion pounds ($102 billion)
against more than 120 billion pounds in April.

June 14 - Obama, makes a fourth trip to the Gulf.

-- 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 - Lawmakers summon top executives from Exxon Mobil
(XOM.N), Chevron (CVX.N), ConocoPhillips (COP.N), Royal Dutch
Shell (RDSa.L) and BP.

-- Obama says in his first televised speech from the Oval
Office: "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."

June 16 - BP agrees to set up a $20 billion fund for damage
claims from the spill, 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 faces the wrath of U.S. lawmakers as he
appears before a congressional hearing. He apologizes for the
spill and says everything is being done to stop it. Members of
Congress accuse BP of cutting corners for the sake of profit.

June 18 - Anadarko Petroleum (APC.N), part owner of the
gushing well, says BP's behavior before the blowout was
"reckless" and likely represented "gross negligence or willful
misconduct" that would affect obligations of the well owners.

June 20 - Internal BP document released by U.S. congressman
shows BP estimates that a worst-case scenario rate could be
100,000 barrels (4.2 million gallons/15.9 million liters) a
day. This is far higher than the U.S. government estimate of
60,000 barrels (2.5 million gallons/9.5 million liters) a day.

June 22 - Hayward is handing day-to-day control of the
spill operation to Bob Dudley -- a reflection, says BP, of the
need for the CEO to return to other aspects of the business.

June 24 - A U.S. judge refuses to put on hold his decision
to lift a ban on deepwater drilling imposed after the spill.

June 28 - BP is forced to defend its chief executive after
Russia's deputy prime minister said he expected Hayward to
resign soon.

June 30 - Hurricane Alex, later downgraded to a tropical
storm, moved slowly in Gulf waters, disrupting the cleanup, and
threatening to push more oily water onshore.

-- President Obama formally directs officials to draw up a
long-term economic and environmental plan to help the Gulf
Coast region get back on its feet after the oil spill.

July 1 - BP shares gain, with traders initially citing
talk, quickly shot down, that it had capped the leaking well.

July 3 - A supertanker converted into a "super skimmer"
begins tests. The vessel can remove up to 500,000 barrels (21
million gallons/79.5 million liters) of oil and water from the
sea surface a day.

July 5 - BP says that the cost of the spill had reached
$3.12 billion.

July 6 - Summer storms push oil from the Gulf of Mexico
spill deeper into Louisiana's wetlands and temporarily slow
efforts to contain damage.

July 7 - Tests show tar balls washed up on the Texas coast
are from the spill, meaning every U.S. Gulf state -- Louisiana,
Mississippi, Alabama, Florida and now Texas -- has been soiled
by the spill.

July 12 - BP installs a "capping stack," which has a better
seal than the last cap placed on the well and aims to stop oil
from spewing out.

-- BP starts shutting a sequence of valves after getting
approval from the U.S. government, delaying testing by 24 hours
on fears the process could irreparably damage the well. BP
starts a critical pressure test to gauge pressure in its
gushing well on July 14.

July 15 - BP is to launch a critical pressure test on the
well after fixing a leak that had halted the operation.
(Writing by David Cutler, London Editorial Reference Unit)