A drilling rig or oil rig is a structure housing equipment used to drill for and extract oil or natural gas from underground reservoirs.

The term can refer to a land-based rig, or a marine-based structure commonly called an 'offshore rig'. The term correctly refers to the equipment that drills the oil well including the rig derrick (which looks like a metal frame tower). Laypeople also refer to the structure upon which the rig sits and from which the wells produce as a 'rig', but this is not correct. The correct name for the structure in an marine environment is the platform. A structure upon which wells produce is a production platform. A floating vessel upon which a drilling rig sits is a floating rig or semi-submersible rig because the whole purpose of the structure is for drilling.

Drilling rigs can be vast, capable of drilling through thousands of metres of the Earth's crust; large "mud pumps" are used to circulate drilling mud (liquid bentonite clay with high barium sulfate content) through the drill bit and the casing, for cooling and removing the "cuttings" whilst a well is drilled; hoists in the rig can lift thousands of tons of pipe; other equipment can force acid or sand into reservoirs to facilitate extraction of the oil; and permanent living accommodation and catering for crews which may be greater than a hundred people in number. Marine rigs may operate many hundreds of miles or kilometres offshore with infrequent crew rotation.

The drilling and production of oil and gas pose a safety risk and a hazard to the environment from the ignition of the entrained gas causing dangerous fires and also from the risk of oil leakage polluting water, land and groundwater. For these reasons, redundant safety systems and highly trained personnel are required by law in all countries with significant production.

See also

• Oil platform