Marine drilling operations are undertaken primarily by mobile offshore drilling units (MODUs). MODUs can be of two basic types, bottom-supported or floating. Bottom-supported MODUs include jackups and submersibles. Floating MODUs include semisubmersibles, drillships, offshore barges and tender-assisted units, which generally are built with semisubmersible or barge hulls.
Other types of drilling rigs are used in marine drilling operations, including inland water drill barges and platform rigs.