A rig explosion killed 11 workers and spewed oil for nearly three months in April, 2010.

The US Justice Department has reached an $18.7 ($24.5) billion agreement with BP to settle civil claims arising from the 2010 Deepwater Horizon oil spill in the Gulf of Mexico – the worst oil spill in US history.

The agreement comes five years and 73 days after the blowout in 2.6-kilometre deep water led to an explosion aboard the Deepwater Horizon that killed 11 people and immolated the giant rig. There had never been a blowout at such depths, and initial efforts to shut in the well failed.

"If approved by the court, this settlement would be the largest settlement with a single entity in American history," Attorney General Loretta Lynch said. "It would help repair the damage done to the Gulf economy, fisheries, wetlands and wildlife. And it would bring lasting benefits to the Gulf region for generations to come."

The rig sank on April 22, 2010, coming to rest upside down on the muddy floor of the Gulf about 500 metres from the wellhead. The Macondo well continued to gush for a total of 87 days, polluting the gulf with millions of barrels of oil – the precise amount became the focus of furious legal battling – before it could be capped by new hardware and shut in.

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The legal repercussions have been lengthy and complicated. The agreement addresses the most critical unresolved issue: How much BP must pay in Clean Water Act fines.

According to the agreement, BP will pay $US5.5 billion ($7.21 billion) in Clean Water Act penalties, 80 per cent of which will go to restoration efforts in the five affected Gulf states: Alabama, Florida, Louisiana, Mississippi and Texas. It will also pay $US8.1 billion ($10.61 billion) in natural resource damages and an additional $US700 million ($917 million) to respond to environmental damages unknown at the time of the agreement.

BP has also agreed to pay $US5.9 billion ($7.73 billion) to settle claims by state and local governments for economic damages suffered as a result of the spill, and a total of $US600 million ($786) for other claims, including for reimbursement of damage assessment costs.

"This is a landmark settlement," Alabama Governor Robert Bentley of Alabama said. "It is designed to compensate the state for all the damages, both environmental and economic."

Washington Post, New York Times