BP is due in court in New Orleans on Monday, before a judge who will decide who is to blame, and to what extent, for the Deepwater Horizon oil disaster, the BBC reported.
The case could last two years and BP could be fined roughly $17.6 billion if the judge finds the company guilty of gross negligence in the 2010 oil spill in the Gulf of Mexico.
The final payouts that BP and the other firms involved will owe in civil penalties and to the victims are still largely an open question, CNN reported.
In addition to the roughly $17 billion in civil penalties, BP could end up paying tens of billions more to the victims, said Edward Sherman, a professor at Tulane Law School in Louisiana.
The Deepwater Horizon oil rig exploded in the Gulf in April 2010, killing 11 workers and releasing five million barrels of crude oil from BP's Macondo well.
US President Barack Obama called the spill "the worst environmental disaster the nation has ever faced."
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So far the company has paid out $7.5 billion in clean-up costs and compensation and BP chief executive Bob Dudley said the company is ready for a lengthy court battle.
Dudley, who took over from former chief executive Tony Hayward, told Britain's Sunday Telegraph that BP can continue to function for years and has set aside $40 billion for the fines.
Hayward resigned amid criticism over the way he had handled the oil spill.
The Telegraph also reported that lawyers for the UK firm will argue that other organizations such as Halliburton and Transocean, the owner of the Deepwater Horizon rig, bear responsibility for the spill. Both are defendants in the trial.
"No single action, person or party was the sole cause of the blowout,” said Mike Brock of Covington & Burling, trial counsel for BP. “BP did not engage in any gross negligence or wilful misconduct.”