BP faces a fine of up to US$13.7bn (£9bn) after a US judge ruled that the 2010 Gulf of Mexico oil spill was smaller than initially feared.
His ruling put the spill at 3.2 million bbls - the US government had estimated it at 4.09 million bbls.
It shields the oil giant from what could have been a US$17.6bn fine. A final figure is expected later this month.
The case relating to the aftermath of the Deepwater Horizon drilling rig explosion was heard in New Orleans.
In his ruling the judge said BP's response to the disaster had not been grossly negligent.
However, he stuck to his earlier decision that it had been grossly negligent leading up to the explosion, in which 11 men aboard the drilling rig were killed.
BP is appealing against that decision.
These latest penalties under the US Clean Water Act would be in addition to more than US$42 billion BP has set aside or spent already on clean-up, compensation and fines.
The company has sold at least US$39 billion in assets since the spill.
In 2012, BP accepted criminal responsibility for the disaster and agreed to pay US$4.5 billion to the US government, thus settling its criminal liability in the spill.
These latest legal efforts have focused on the amount of civil penalties the firm must pay, both to businesses and individuals affected by the spill and to cover environmental clean-up costs.
In a short statement released on Friday, BP said that it "is continuing to review the court's decision".
US-listed shares of BP rose about 1% to US$36.20 in after-hours trading.
Source: BBC News
Adapted from source by Joe Green