BP is required to cover some -- but not all -- of rig owner Transocean's liabilities in the massive 2010 oil spill in the Gulf of Mexico, a US judge ruled Thursday.

The mixed ruling found that BP must indemnify its subcontractor for compensatory damages even if the claim is a result of Transocean's negligence. But BP does not need to cover any punitive damages or civil penalties that may be assessed, the 30-page ruling said.