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An explosion aboard the Deepwater Horizon drilling rig in the Gulf of Mexico, 52 miles south-east of Venice, Louisiana, kills 11 workers. Operator Transocean, BP, says it had no warning of trouble ahead of the blast.The rig was drilling in about 5,00 of water, pushing the boundaries of deepwater drilling tech.
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President Obama makes his first trip to the Gulf Coast and says BP is responsible for the leak and for paying for its clean-up.
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Researchers who have analysed underwater video from the leak site estimate as many as 70,000 barrels of oil are leaking into the Gulf per day, with a margin of error of plus or minus 20%, significantly higher than earlier estimates.
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Carol Browner, President Barack Obama's adviser on energy policy, says the spill is the worst environmental disaster in US history, worse even than the 1989 Exxon Valdez spill in Alaska.
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The US government says underwater oil plumes have travelled as far as 40 miles from the site of the leaking well.
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President Obama addresses the nation from the Oval Office, vowing, "We will make BP pay for the damage their company has caused."
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Officials said it was unclear if the oil had drifted hundreds of kilometres from the leak site to the Texas shore, or had fallen from ships taking part in the clean-up operation.
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BP confirms that chief executive Tony Hayward will leave his post by mutual agreement in October, but he is likely to retain a position in the company.
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BP announces that the total cost to it of the oil spill so far has reached $6.1bn (£3.8bn). The total includes the cost of the spill response, containment, relief well drilling, and cementing up of the damaged well.
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The ruptured well is finally sealed and "effectively dead", says the top US federal official overseeing the disaster, Coast Guard Adm Thad Allen.
