| Abbreviation | Definition |
|---|---|
| ORRR | Ontario & Rainy River Railway |
| OSCZ | Intermodal Services Inc. |
| OSCZ | Intermodal Services Incorporated |
| OSHR | Ontario, Simcoe, & Huron Railway |
| OSL | Oregon Short Line (Union Pacific Railroad) |
| OSRR | Ohio Southern Railroad |
| OSRR | Ohio Southern Railroad Incorporated |
| OSRX | Ontario Southland Railway |
| OSRX | Ontario Southland Railway Incorporated |
| OSSU | Eurovos B.V. |
| OSSU | Eurovos, B. V. |
| OTCO | Owensville Terminal |
| OTCO | Owensville Terminal Company |
| OTCR | Oakdale Traction Corporation |
| OTDX | Greenbrier Leasing Corporation |
| OTPU | Seacube Container Leasing |
| OTPX | Otter Tail Power |
| OTR | Oakland Terminal Railway |
| OTRX | On-Track Railway Services |
| OTRX | On-Track Railway Services Limited |