- O&M—Operation and Maintenance Expenses
- O3—Ozone
- OASIS—Open Access Same-Time Information System
- OATT—Open Access Transmission Tariff (US)
- OCS—Outer Continental Shelf (oil)
- OCSLA—Outer Continental Shelf Lands Act (oil)
- OECD—Organization for Economic Cooperation and Development
- OEM—original equipment manufacturers
- OFO—Operational Flow Order
- OMP—Operation and Maintenance Plan
- Ontario—IESO Ontario Independent Electricity System Operator (Canada)
- OPEC—Organization of Petroleum-Exporting Countries (oil)
- OPRG—oxygenated fuels program reformulated gasoline (oil)
- ORNL—Oak Ridge National Laboratory (U.S.) (nuclear)
- OSHA—U.S. Department of Labor Occupational Safety and Health Administration
- OTAG—Ozone Transport Assessment Group
- OTDF—Outage Transfer Distribution Factor
- OTEC—ocean thermal energy conversion (electricity)
Read more about this topic: List Of Energy Abbreviations