| Abbreviation | Definition |
|---|---|
| OFIA | Ontario Forest Industry Association |
| OFVGA | Ontario Fruit and Vegetable Growers' Association |
| OGA | New Hampshire Old Graveyard Association |
| OGA | Oregon Geographic Alliance |
| OGA | Outdoor Guides Association |
| OGA-NA | Outdoor Guides Association of North America |
| OHE | Organization of Healthcare Educators |
| OHG | Operators Harmonization Group |
| OHPA | Oral Health Professionals Association |
| OHRIA | Ontario Horse Racing Industry Association |
| OHSM | Occupational Health and Safety Management |
| OHT | Ohio History Teachers |
| OHT | Organization of History Teachers |
| OIA | Ontario Institute of Agrologists |
| OIC | Open Interchange Consortium |
| OIC | Options Industry Council |
| OIE | Office International des Epizooties |
| OIEA | Onferenceoregon Indian Education Association |
| OIEA | Oregon Indian Education Association |
| OIML | Organisation Internationale de Métrologie Légale (International Organization of Legal Metrology) |