| Abbreviation | Definition |
|---|---|
| OPSX | Public Service Company of Oklahoma |
| OPSX | Public Service of Oklahoma |
| OPT | Orange Port Terminal Railway |
| OPTU | Optimodal |
| OPX | Ohio Power |
| OPX | Ohio Power Company |
| OQR | Ontario & Quebec Railway |
| OR | Owasco River Railway |
| ORA | Ormet Railroad |
| ORA | Ormet Railroad Corporation |
| ORBIS | Offering Rail Better Information Systems |
| ORC | Old Recycled Caboose |
| ORCU | BSL Transport |
| ORDC | Ohio Rail Development Commission |
| OREX | Oregon Department of Agriculture |
| ORHF | Oregon Rail Heritage Foundation |
| OROX | U.S. Department of Energy Oak Ridge Operations |
| OROX | United States Department of Energy Oak Ridge Operations Office |
| ORR | Office of Rail regulations |
| ORR | Osage Railroad |