A – B – C – D – E – F – G – H – I – J – K – L – M – N – O – P – R – S – T – U – V – W – X
| OBEVA | OBDT Evaluation Report |
| OBDTL | OBDT Log |
| OBCS | Ocean Bottom Cable System |
| OBC | Ocean-bottom cable (seismic collection) |
| OCSLA | OCS Lands Act |
| OT | Off Tree |
| ONRR | Office of Natural Resources Revenue |
| ONNR | Office of Natural Resources Revenue (formerly MMS) |
| OFST | Offset Vertical Seismic Profile |
| OVSP | Offset vertical seismic profiling |
| OIM | Offshore installation manager |
| OOE | Offshore Operation Engineer (senior technical authority on an offshore oil platform) |
| OOC | Offshore Operators Committee |
| OPITO | Offshore Petroleum Industry Training Organization |
| OSV | Offshore support vessel |
| OTC | Offshore Technology Conference |
| OVID | Offshore Vessel Inspection Database |
| O&G | Oil and Gas |
| OCIMF | Oil Companies International Marine Forum |
| OCI | Oil Corrosion Inhibitor (Vessels) |
| OCTG | Oil country tubular goods |
| ODT | Oil Down To |
| OIP | Oil in place |
| OML | Oil mining lease |
| ONAN | Oil Natural Air Natural cooled transformer |
| Brownfields | Oil or gas fields that are beyond their production plateau but are still producing |
| SO | Oil saturation |
| OSCP | Oil spill contingency plan |
| OSFR | Oil spill financial responsibility |
| OSLTF | Oil Spill Liability Trust Fund |
| OSRO | Oil spill response organization |
| OSRP | Oil spill response plan |
| OSRV | Oil spill response vessels |
| OSRAM | Oil Spill Risk Analysis Model |
| OSRA | Oil spill risk assessment |
| OUT | Oil Up To |
| OWC | Oil Water Contact |
| Sweet | Oil/gas that has low sulfur content |
| Sour | Oil/gas with high sulfur content |
| OWR | Oil/water ratio |
| OBM | Oil-Based Mud |
| OWC | Oil-Water Contact |
| OTJ | On the job |
| OTSG | One time Through Steam Generator |
| 1D | One-dimensional (usually a checkshot seismic survey) |
| OSC | On-scene coordinator |
| MOMR | OPEC Monthly Oil Market Report |
| ORB | OPEC reference basket (of crudes) |
| OH | Open hole |
| OHC | Open Hole Completion |
| OHGP | Openhole gravel pack |
| OH | Openhole Log |
| OPEX | Operating expenditure |
| OP | Operating procedure |
| OTIP | Operational Testing Implementation Plan |
| O&M | Operations and Maintenance |
| OPL | Operations Log |
| OPS | Operations Report |
| OTL | Operations Team Leader |
| OTDR | Optical Time Domain Reflectometry |
| OECD | Organization for Economic Co-operation and Development |
| OAPEC | Organization of Arab Petroleum Exporting Countries |
| OPEC | Organization of Petroleum Exporting Countries |
| ORICO | Oriented Core Data Report |
| OMRL | Oriented Micro-Resistivity Log |
| OEM | Original Equipment Manufacturer |
| OOIP | Original oil in place |
| ORM | Other regulated materials (a DOT materials classification) |
| OOS | Out of service |
| OOT | Out of Tolerance |
| OCS | Outer Continental Shelf |
| OD | Outer Diameter (of a tubular component such as casing) |
| OUT | Outpost, Lahee classification |
| OS&D | Over, Short & Damage (Report) |
| OB | Overbalanced |
| OPRES | Overpressure Log |
| OVCH | Oversize Charts |
| OT | Overtime |
| OI | Oxygen Index |