| Abbreviation | Definition |
|---|---|
| CNYK | Central New York Railroad Corporation |
| CNYX | Central New York Locomotive |
| CNZR | Central New England Railroad |
| CNZR | Central New England Railroad Company |
| CO | Chesapeake and Ohio Railway (CSX Transportation) |
| CO | CSX Transportation Incorporated |
| COAX | Trinity Rail Management |
| COAX | Trinity Rail Management Incorporated |
| COBX | Cobre Mining |
| COBX | Cobre Mining Company Limited |
| COCX | Chevron Oronite |
| COE | Colorado and Eastern Railroad |
| COEH | Conecuh Valley Railroad |
| COER | American Rail Heritage - Crab Orchard and Egyptian Railroad |
| COER | Crab Orchard and Egyptian Railroad |
| COEZ | Crab Orchard and Egyptian Railroad |
| COFC | Container On FlatCar |
| COLU | XTRA Intramodal |
| COLX | Collins Construction Co. (Alliant Energy) |
| COLX | Wisconsin Power and Light Company |