| Abbreviation | Definition |
|---|---|
| UNCX | CGTX Incorporated |
| UNCX | Union Carbide Canada |
| UNI | Unity Railways |
| UNPX | Procor Limited |
| UNPX | Union Petroleum (Procor) |
| UNSX | MidAmerican Energy Company |
| UNSX | Unitrain Services |
| UNTX | MRC Rail Services LLC |
| UNTX | Unitrain (MRC Rail Services) |
| UO | Union Railroad of Oregon |
| UOCX | General American Marks Company |
| UOCX | Union Oil Co. of California (GATX) |
| UOEX | Uno-ven |
| UOPX | U O P, A New York Partnership |
| UOPX | UOP New York |
| UP | Union Pacific Railroad |
| UP | Union Pacific Railroad Company |
| UP | Union-Pearson |
| UPAX | United Power Association |
| UPB | Union Pacific Railroad |