| Abbreviation | Definition |
|---|---|
| O39 | Oversea-Chinese Banking Corp. Limited |
| O4D | Open For Developers |
| OA | Olympic Airways |
| OA | Oriental Adventures |
| OAA | Ogden, Allen, and Associates |
| OAC | Orbital Assembly Corporation |
| OACL | ORIX Australia Corporation Limited |
| OACM | Overseas Assurance Corporation Malaysia |
| OAE | Outdoor Advertising Exchange |
| OAF | Orlando Advertising Federation |
| OAI | Optical Associates Incorporated |
| OAI | Optimization Associates Inc |
| OAI | Orr Associates Inc |
| OALA | Obleek Apparel Los Angeles |
| OAN | OCEANIE / AFRIQUE NOIRE FINE ART BOOKS |
| OAN | Open Air Networks |
| OANDO | Ocean and Oil Limited |
| OAR | Oxford Applied Research |
| OARS | Outdoor Adventure River Specialists |
| OAS | Oshikai Advertising Services |