| Abbreviation | Definition |
|---|---|
| APRX | Air Products and Chemicals Incorporated |
| APSU | Altorfer Power Systems |
| APSX | Arizona Public Service |
| APTX | Air Products and Chemicals |
| APTX | Air Products and Chemicals Incorporated |
| APWX | Appalachian Power |
| APWX | Appalachian Power Company |
| APXX | Alberta Prairie Rail Excursions |
| APXX | Alberta Prairie Railway Excursions |
| APXX | Associated Packers (Cementos Apasco) |
| AQCX | Aqua-Chem (Celaver Brooks Division) |
| AQCX | Aqua-Chem Incorporated Cleaver Brooks Division |
| AR | Aberdeen and Rockfish Railroad |
| AR | Aberdeen and Rockfish Railroad Company |
| AR | All Rail |
| ARA | Arcade and Attica Railroad |
| ARA | Arcade and Attica Railroad Corporation |
| ARB | Arth-Rigi-Bahn |
| ARC | Alexander Railroad |
| ARC | Alexander Railroad Company |