| Abbreviation | Definition |
|---|---|
| GMCX | General Motors Corporation |
| GMDX | General Motors Diesel Canada |
| GMGX | M and G Polymers USA |
| GMHX | General American Marks (GATX Corporation) |
| GMIX | Chicago Freight Car Leasing Company |
| GMIX | General Mills (Chicago Freight Car Leasing) |
| GMO | Gulf, Mobile and Ohio Railroad (Canadian National Railway) |
| GMO | Illinois Central Railroad Company |
| GMPR | Goods Movement Ports and Rail |
| GMPTA | Greater Manchester Passenger Transport Authority |
| GMRC | Green Mountain Railroad |
| GMRC | Green Mountain Railroad Corporation |
| GMRY | Great Miami and Scioto Railway |
| GMRY | Great Miami and Scioto Railway Company |
| GMSG | German Shanghai Metro Group |
| GMSR | Gulf & Mississippi Railroad (Kansas City Southern Railway) |
| GMSR | Kansas City Southern Railway Company |
| GMTX | General American Marks (GATX Corporation) |
| GN | Burlington Northern and Santa Fe Railway Company |
| GN | Great Northern Railway (BNSF Railway) |