| Abbreviation | Definition |
|---|---|
| OCSU | Scripps Institute of Oceanography |
| OCTL | Oil Creek and Titusville Lines |
| OCTR | Octoraro Railway |
| OCTR | Octoraro Railway Incorporated |
| OCTX | Octel America |
| OCTX | Octel America Incorporated |
| ODTX | Oil-Dri Corporation of America |
| OEDX | Ohio Edison |
| OFCX | Ortner Freight Car |
| OFCX | Residco |
| OFOX | Residco |
| OFSX | Tucson Electric Power |
| OFSX | Tucson Electric Power Company |
| OGEE | Ogeechee Railway |
| OGEE | Ogeechee Railway Company |
| OGEX | Oklahoma Gas and Electric |
| OGEX | Oklahoma Gas and Electric Company |
| OGSX | IES Utilities Incorporated |
| OGSX | Iowa Southern Utilities |
| OGTU | Orphan Grain Train |