| Abbreviation | Definition |
|---|---|
| MIDH | Middletown and Hummelstown RR Company |
| MIDL | Midland Railway |
| MIDX | M R C Rail Services, L. L. P. |
| MIDX | MRC Rail Services |
| MIEU | MI Engineering |
| MIEU | MI Engineering Limited |
| MIGN | Michigan Northern Railway |
| MILW | Chicago, Milwaukee, St. Paul and Pacific Railroad (Canadian Pacific Railway) |
| MILW | Soo Line Railroad Company |
| MILX | General Electric Railcar Services Corporation |
| MILX | Milchem (GE Rail Services Corporation) |
| MILZ | Chicago, Milwaukee, St. Paul and Pacific Railroad (Canadian Pacific Railway) |
| MILZ | Soo Line Railroad Company |
| MIMX | Minera Mexico Internacional Incorporated |
| MIMX | Minera Mexico International |
| MINE | Minneapolis Eastern Railway |
| MINU | China Ocean Shipping |
| MINU | China Ocean Shipping Company |
| MIPX | Millennium Petrochemicals |
| MIR | Minneapolis Industrial Railway |