| 1 | SOU | Southern Airways | Callsign: Southern Express, | USA | AVCODES |
| 2 | SOU | South Pacific Airlines Ltd. | Callsign: Paradise, | HK | AVCODES |
| 3 | SOU | Southern Airways | | | ICAO1 |
| 4 | SOU | Southern Ry. System | 1/1975-1/1980; eliminated 1/1991 | | NAKINA |
| 5 | SOU | Norfolk Southern Ry. Co. | added 1/1991; 1/1994-7/2005 | | NAKINA |
| 6 | SOU | Southern Ry. System | 1/75-1/80; eliminated 1/91 | | NRHS |
| 7 | SOU | Norfolk Southern Ry. Co. | added 1/91; 1/94-7/2000 | | NRHS |
| 8 | SOU | NORFOLK SOUTHERN RAILWAY COMPANY [SOUTHERN RY.] | | | PWRC |
| 9 | SOU | Southern Railway (Norfolk Southern Railway) | | | RSRV |
| 10 | SOU | Southern Railway System | | USA | TRAFFIC |
| 11 | SOUE | SOUTHERN TRANSPORTATION LLC | | | SCAC4 |
| 12 | SOUE | Southend Corporation | | GB | TRAFFIC |
| 13 | SOUK | SOUTHVIEW TRUCKING LTD | | | SCAC4 |
| 14 | SOUL | SOURCE ONE TRANSPORTATION LLC | | | SCAC4 |
| 15 | SOUQ | SOUTHERN TRUCKING COMPANY INC | | | SCAC4 |
| 16 | SOUS | SOUNION SPECIAL MARITIME ENTERPRISE | | | SCAC4 |
| 17 | SOUTR | Southern Transit Bus Company | | GB | TRAFFIC |
| 18 | SOUTST | Southeastern Stages | A Greyhound subsidiary | USA | TRAFFIC |
| 19 | SOUU | SOUILLAC INDUSTRIES LTD. | | MUS | BIC |
| 20 | SOUU | NORFOLK SOUTHERN RAILWAY COMPANY [SOUTHERN RY.] | | | PWRC |
| 21 | SOUU | Southern Railway (Norfolk Southern Railway) | | | RSRV |
| 22 | SOUW | SOUTHWEST FREIGHT INC | | | SCAC4 |
| 23 | SOUX | CIT Group/Capital Finance Inc. | added 7/2009 | | NAKINA |
| 24 | SOUX | THE CIT GROUP/CAPITAL FINANCE INC | | | SCAC4 |
| 25 | SOUY | ST LOUIS CONSOLIDATORS INC | | | SCAC4 |
| 26 | SOUZ | NORFOLK SOUTHERN RAILWAY COMPANY [SOUTHERN RY.] | | | PWRC |
| 27 | SOUZ | NORFOLK SOUTHERN RAILWAY COMPANY (N | | | SCAC4 |
