BP Plc faces billions more in potential penalties after a judge found it acted with gross negligence in the 2010 Gulf of Mexico oil spill, dealing a blow to the company's efforts to expand its drilling program as costs rise and production slips. In a turning point after four years of legal wrangling over responsibility, U.S. District Judge Carl Barbier's ruling laid the bulk of the blame on BP for the explosion, which killed 11 men and caused the largest offshore oil spill in U.S. history.