| Abbreviation | Definition |
|---|---|
| AOIX | Ashland Oil (Marathon Petroleum) |
| AOIX | Ashland Petroleum Company |
| AOK | Arkansas-Oklahoma Railroad |
| AOK | Arkansas-Oklahoma Railroad Incorporated |
| AONU | NEC Energy Solutions |
| AOR | Aliquippa and Ohio River Railroad |
| AOUX | Alberta and Orient Glycol |
| AOUX | Alberta and Orient Glycol Company Limited |
| APA | Apache Railway |
| APA | Apache Railway Company |
| APAU | APR Energy |
| APAX | Associated Packers (Cementos Apasco) |
| APAX | Cementos Apasco S.A. de C.V. |
| APAXX | Associated Packers (Cementos Apasco) |
| APB | Absolute Permissive Block |
| APCU | American President Lines |
| APCU | American President Lines Limited |
| APCX | Allied Lime Company |
| APCX | Allied Products (Allied Lime) |
| APD | Albany Port District |