===== Terms beginning with O =====

[[Occupational Safety and Health Administration]]

[[OCS]]

[[Offset well]]

[[Offshore drilling]]

[[Ohm]]

[[Ohmic]]

[[Ohm meter|Ohm-meter]]

[[Ohm's law]]

[[Oil base mud|Oil-base mud]]

[[Oil cut|Oil-cut]]

[[Oil emulsion]]

[[Oil field]]

[[Oil in place]]

[[Oil mud]]

[[Oil patch]]

[[Oil shale]]

[[Oil stain]]

[[Oil water contact|Oil-water contact]]

[[Oil water interface|Oil-water interface]]

[[Oil wet]]

[[Oleophilic]]

[[Open hole]]

[[Openhole completion]]

[[Operator]]

[[OSHA]]

[[Osmosis]]

[[Outcrop]]

[[Overburden]]

[[Overlay]]

[[Overpressure]]

[[Overshot]]

[[Oxidation reduction potential|Oxidation-reduction potential]]