| 1 | SLO | Edgartown Air, Inc. | Callsign: Slow, | USA | AVCODES |
| 2 | SLO | Slocum Air, Inc. | Callsign: Slocum, | USA | AVCODES |
| 3 | SLO | Edgartown Air | | | ICAO1 |
| 4 | SLOA | SOLANO RAMOS, OSCAR | | | SCAC4 |
| 5 | SLOB | SOUTHERN LOGISTICS | | | SCAC4 |
| 6 | SLOF | (The) St. Louis and O'Fallon Ry. (Co.) | 8/1920-7/1954 | | NAKINA |
| 7 | SLOF | St. Louis and O'Fallon Ry. | 4/38-1/52 | | NRHS |
| 8 | SLOF | ST. LOUIS & O'FALLON RWY. | | | PWRC |
| 9 | SLOI | SWAN & HERCULES GLOBAL LOGISTICS CO | | | SCAC4 |
| 10 | SLOJ | SALSON LOGISTICS INC | | | SCAC4 |
| 11 | SLOK | SHUR LOK PRODUCTS | | | SCAC4 |
| 12 | SLOL | ST. LOUIS, IRON MOUNTAIN & SOUTHERN | | | PWRC |
| 13 | SLON | South London | | GB | TRAFFIC |
| 14 | SLOP | SOLORIOS TRUCKING | | | SCAC4 |
| 15 | SLOQ | SOLOI INC | | | SCAC4 |
| 16 | SLOR | SELECT ONE (1) TRANSPORT INC | | | SCAC4 |
| 17 | SLOS | SUPERIOR LOGISTICAL SERVICES INC | | | SCAC4 |
| 18 | SLOT | SHOWA LINE, LTD. | | | PWRC |
| 19 | SLOT | SUPREME LOGISTICS INC | | | SCAC4 |
| 20 | SLOU | SHIPWAVES ONLINE LLC | | UAE | BIC |
| 21 | SLOU | SHOWA LINE, LTD. | | | PWRC |
| 22 | SLOU | Showa Line Limited | | | RSRV |
| 23 | SLOVN | SLOVNAFT, a.s. | | SK | VKM |
| 24 | SLOX | Sunland Oil Co. | 8/1920 | | NAKINA |
| 25 | SLOX | Selox, Inc. | added 1/1984; eliminated 7/1992 | | NAKINA |
| 26 | SLOX | Selox, Inc. | eliminated 7/92 | | NRHS |
| 27 | SLOX | *SUNLAND OIL CO. | | | PWRC |
| 28 | SLOX | *RETIRED 07-08-92 (1393) ATP [SELOX INC.] | | | PWRC |
| 29 | SLOX | Selox | | | RSRV |
