Oil giant BP has taken legal steps to cut the civil damages it faces for the Deepwater Horizon disaster by up to 3.4bn dollars.

The firm has asked a New Orleans court hearing the case against it for civil penalties and damages to rule that at least 810,000 barrels of oil had been captured during the spill and it should not be fined for them.

The Deepwater Horizon rig, which was leased by BP, exploded on April 20th 2010, killing 11 workers and leading to one of the worst environmental disasters in US history.

Under the US Clean Water Act each barrel of oil spilled can result in a fine of up to $4,300 if the guilty party is found to have acted with gross negligence.

The US attorney-general, Eric Holder, has already said he intends "to prove that BP was grossly negligent in causing the oil spill", something the company denies.

BP could face a fine of up to $21bn based on the US government's estimate that 4.9m barrels of oil escaped from the well.

The firm argues that it captured 810,000 barrels-worth escaping from the Macondo well and claims it should not "be penalised for not only trying to do the right thing, but successfully doing the right thing and keeping oil out of the marine environment".

If the court accepts the argument it could reduce the maximum possible fine to $17.6bn.

BP struck a deal with the US government in November, which will see it pay $4.5bn, including a $1.26bn criminal fine.

The oil giant has already spent $14bn on cleaning up the oil spill and compensation to local people and businesses.

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