| Abbreviation | Definition |
|---|---|
| ONJ | OceanNJ |
| ONM | One Night Magic |
| ONMJ | O'Donnell, Naccarato, Mignogna, & Jackson, Inc. |
| ONTAP® | ONline Training And Practice ELSEVIR |
| ONU | ONDEO NALCO University |
| OOBE | Out Of Business Entirely |
| OOC | Ober Oil Company |
| OOC | Ohio Oil Company |
| OOC | Oman Oil Company |
| OOC | Operations Control Centre |
| OOCL | Orient Overseas Container Line |
| OOD | Offshore One Design |
| OODA | O'Donnell O'Neill Design Associates |
| OOG | Österreichische OffiziersGesellschaft |
| OOI | Ohio Online, Inc. |
| OOI | Open Object, Inc. |
| OOIL | Orient Overseas International Ltd |
| OOL | Optimum On-Line |
| OOMCO | Oman Oil Marketing Company (est. 2003) |
| OOO | Open Office. Org |