| Abbreviation | Definition |
|---|---|
| MPLZ | Missouri Pacific Railroad (Union Pacific Railroad) |
| MPLZ | Union Pacific Railroad Company |
| MPPR | Petra, The Highlands (Railway station code) |
| MPRC | Missouri Pacific Railroad Company |
| MPRX | Motive Power & Equipment Solutions |
| MPSX | Missouri Public Service |
| MPTX | Magnolia Provision Co. (Procor) |
| MPTX | Procor Limited |
| MPU | Missouri Pacific Railroad |
| MPU | Missouri Pacific Railroad (Union Pacific Railroad) |
| MPWX | Muscatine Power and Water |
| MPZ | Missouri Pacific Railroad (Union Pacific Railroad) |
| MPZ | Union Pacific Railroad Company |
| MQCX | Monarch Cement |
| MQGX | Morrison-Quirk Grain Corporation |
| MQPX | Millennium Inorganic Chemicals |
| MQT | Marquette Rail |
| MR | Malayan Railway |
| MR | McCloud Railway Company |
| MR | McCloud River Railroad (McLeod Railway) |