Drilling for oil in an ocean or large lake. A drilling unit for offshore operations may be a mobile floating vessel with a ship or barge hull, a semisubmersible or submersible base, a self-propelled or towed structure with jacking legs (jack-up drilling rig), or a permanent structure used as a production [[platform]] when drilling is completed. In general, [[wildcat]] wells are drilled from mobile floating vessels (as semisubmersible rigs and drill ships) or from jack-ups. while development wells are drilled from platforms.