RPT-U.S. court says BP 'grossly negligent' in 2010 spill, billions in fines loom

HOUSTON, Sept 4 (Reuters) - A federal judge has found oil giant BP Plc "grossly negligent" for its role in the 2010 spill in the Gulf of Mexico, a ruling that could add billions of dollars in fines to the more than $42 billion in charges taken so far for the worst offshore disaster in U.S. history.