| Abbreviation | Definition |
|---|---|
| OAAS | Ontario Association of Agricultural Societies |
| OAC | Obesity Action Coalition |
| OAC | Ontario Arts Council |
| OAFC | Ohio Association of Free Clinics |
| OAFC | Ongoing Ambassadors For Christ |
| OAGRP | Organization for the Advocacy of the Genocide of Retarded People |
| OAL | Ohio Art League |
| OAR | Organization for Autism Research |
| OASD | Ostomy Association of San Diego |
| OASIS | Older Adult Service Information System |
| OASIS | On-line Asperger's Syndrome Information and Support |
| OASIS | Organization for the Advancement of Structured Information Standards |
| OASIS | Ovarian Awareness, Support, Involvement, and Survivorship |
| OATA | Ontario Art Therapy Association |
| OB | Operation Blessing |
| OBC | Organization for Bat Conservation |
| OBERF | Out of Body Experience Research Foundation |
| OBI | Operation Blessing International |
| OBI | Oxford Baptist Institute |
| OBIR | Operation Blessing International Relief |