British energy giant BP has announced it has agreed to settle US federal and state claims worth up to $US18.7 billion over the 2010 Gulf of Mexico oil spill.

"With this agreement we provide a path to closure for BP and the Gulf," said BP chairman Carl-Henric Svanberg on Thursday.

The agreement increases the pre-tax cost of the disaster to BP by an estimated $US10 billion to $US53.8 billion, the company said, adding that a final figure would be released in its second quarter results due later this month.

"This is a realistic outcome which provides clarity and certainty for all parties," BP group chief executive Bob Dudley added in a statement.

"For BP, this agreement will resolve the largest liabilities remaining from the tragic accident and enable BP to focus on safely delivering the energy the world needs."

The deal has been struck with the US federal government and five Gulf Coast states - Alabama, Florida, Louisiana, Mississippi and Texas - affected by the explosion on the Deepwater Horizon drilling rig.

Eleven people died and millions of barrels of oil were spilled into the Gulf, decimating wildlife and devastating the ecology of a region dependent on the seafood and tourism industries.

The settlement, to be paid out by BP's US upstream subsidiary, BP Exploration and Production Inc, includes $US5.5 billion to the US as a civil penalty under the Clean Water Act.

A further $US7.1 billion will be paid to the US and Gulf Coast states over 15 years for natural resource damages, in addition to $US1 billion already committed.

Another $US4.9 billion will be paid over 18 years to settle economic and other claims made by the five Gulf Coast states.

And up to $US1 billion will be paid to resolve claims made by more than 400 local government entities.

The head of the US Justice Department, Attorney General Loretta Lynch, hailed what she said was a record deal.

"If approved by the court, this settlement would be the largest settlement with a single entity in American history; 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," she said in a statement.