(Bloomberg) – BP Plc acted with gross negligence in setting off the biggest offshore oil spill in U.S. history, a federal judge ruled, handing down a long-awaited decision that may force the energy company to pay billions of dollars more for the 2010 Gulf of Mexico disaster.

U.S. District Judge Carl Barbier held a trial without a jury over who was at fault for the catastrophe, which killed 11 people and spewed oil for almost three months into waters that touch the shores of five states.

“BP has long maintained that it was merely negligent,” said David Uhlmann, former head of the Justice Department's environmental crimes division. He said Barbier “soundly rejected” BP's arguments that others were equally responsible, holding “that its employees took risks that led to the largest environmental disaster in U.S. history.”