| 6301 | SLOA | SOLANO RAMOS, OSCAR | | | SCAC4 |
| 6302 | SLOB | SOUTHERN LOGISTICS | | | SCAC4 |
| 6303 | SLOF | (The) St. Louis and O'Fallon Ry. (Co.) | 8/1920-7/1954 | | NAKINA |
| 6304 | SLOF | St. Louis and O'Fallon Ry. | 4/38-1/52 | | NRHS |
| 6305 | SLOF | ST. LOUIS & O'FALLON RWY. | | | PWRC |
| 6306 | SLOI | SWAN & HERCULES GLOBAL LOGISTICS CO | | | SCAC4 |
| 6307 | SLOJ | SALSON LOGISTICS INC | | | SCAC4 |
| 6308 | SLOK | SHUR LOK PRODUCTS | | | SCAC4 |
| 6309 | SLOL | ST. LOUIS, IRON MOUNTAIN & SOUTHERN | | | PWRC |
| 6310 | SLON | South London | | GB | TRAFFIC |
| 6311 | SLOP | SOLORIOS TRUCKING | | | SCAC4 |
| 6312 | SLOQ | SOLOI INC | | | SCAC4 |
| 6313 | SLOR | SELECT ONE (1) TRANSPORT INC | | | SCAC4 |
| 6314 | SLOS | SUPERIOR LOGISTICAL SERVICES INC | | | SCAC4 |
| 6315 | SLOT | SHOWA LINE, LTD. | | | PWRC |
| 6316 | SLOT | SUPREME LOGISTICS INC | | | SCAC4 |
| 6317 | SLOU | SHIPWAVES ONLINE LLC | | UAE | BIC |
| 6318 | SLOU | SHOWA LINE, LTD. | | | PWRC |
| 6319 | SLOU | Showa Line Limited | | | RSRV |
| 6320 | SLOVN | SLOVNAFT, a.s. | | SK | VKM |
| 6321 | SLOX | Sunland Oil Co. | 8/1920 | | NAKINA |
| 6322 | SLOX | Selox, Inc. | added 1/1984; eliminated 7/1992 | | NAKINA |
| 6323 | SLOX | Selox, Inc. | eliminated 7/92 | | NRHS |
| 6324 | SLOX | *SUNLAND OIL CO. | | | PWRC |
| 6325 | SLOX | *RETIRED 07-08-92 (1393) ATP [SELOX INC.] | | | PWRC |
| 6326 | SLOX | Selox | | | RSRV |
| 6327 | SLP | Salpa Aviation Co. Ltd. (Sudan) | Callsign: Salpa, | SUD | AVCODES |
| 6328 | SLP | Salpa Aviation | | | ICAO1 |
| 6329 | SLPD | ST- LAMBERT (DIV OF TFI TRANSPORT 1 | | | SCAC4 |
| 6330 | SLPE | STEEL & PIPE SUPPLY COMPANY INC | | | SCAC4 |
| 6331 | SLPF | STARLINE LUXURY COACHES | | | SCAC4 |
| 6332 | SLPI | SLADEWSKI PIANO COMPANY | | | SCAC4 |
| 6333 | SLPN | SCHILLI TRANSPORTATION SERVICES INC | | | SCAC4 |
| 6334 | SLPO | SUPER LINK PLASTIC INC | | | SCAC4 |
| 6335 | SLPR | STALLION ENTERPRISES INC | | | SCAC4 |
| 6336 | SLPS | SLIPPER, PAUL | | | SCAC4 |
| 6337 | SLPT | STRUCTURLAM PRODUCTS LTD | | | SCAC4 |
| 6338 | SLPU | SEAGULL CONTAINER SERVICES PTE. LTD. | | SGP | BIC |
| 6339 | SLPV | S & L EXPRESS | | | SCAC4 |
| 6340 | SLQ | Skylink Express Inc | Callsign: Skylink, Formerly QuikAire Cargo Inc. | CDN | AVCODES |
| 6341 | SLQ | St. Lawrence & Atlantic R.R. (Quebec) Inc. | 7/2000-7/2005 | | NAKINA |
| 6342 | SLQ | St. Lawrence & Atlantic R.R. (Quebec) Inc. | Jul-00 | | NRHS |
| 6343 | SLQ | ST. LAWRENCE & ATLANTIC RAILROAD (QUEBEC), INC. | | | PWRC |
| 6344 | SLQ | St. Lawrence and Atlantic Railroad (Genesee & Wyoming) | | | RSRV |
| 6345 | SLQ | ST LAWRENCE & ATLANTIC RAILROAD (QU | | | SCAC4 |
| 6346 | SLQ | St. Lawrence & Atlantic R.R. (Quebec) Inc. | | CDN | TRAFFIC |
| 6347 | SLQA | SELECT TRANSPORT INC | | | SCAC4 |
| 6348 | SLQB | SCS LOGISTICS LLC | | | SCAC4 |
| 6349 | SLQC | STRAIGHT LINE LOGISTICS LLC | | | SCAC4 |
| 6350 | SLQF | SAADCO LOGISTIQUES INC | | | SCAC4 |
| 6351 | SLQH | SOLIS, LORENA ENRIQUEZ | | | SCAC4 |
| 6352 | SLQJ | S LOGISTICS LLC | | | SCAC4 |
| 6353 | SLQK | SLICK | | | SCAC4 |
| 6354 | SLQL | SLAC LOGISTICS LLC | | | SCAC4 |
| 6355 | SLQP | S & L TRANSPORTATION SERVICES INC | | | SCAC4 |
| 6356 | SLQQ | SIMARD, L TRANSPORT LTD | | | SCAC4 |
| 6357 | SLQS | SEAL TRANSPORTATION INC | | | SCAC4 |
| 6358 | SLQT | SHASTA LUMBER TRANSPORT | | | SCAC4 |
| 6359 | SLQV | STARLITE SERVICES INC | | | SCAC4 |
| 6360 | SLQY | SPEEDLINE SYSTEMS INC | | | SCAC4 |
| 6361 | SLR | Sobelair | IATA: Q7, Callsign: Sobelair, Ceased operations | B | AVCODES |
| 6362 | SLR | Silverjet plc | IATA: Y7, Callsign: Silverjet, IATA Prefix: 362, Ceased operations on 30 May 2008. | GB | AVCODES |
| 6363 | SLR | Silverstone Air Services Ltd | IATA: K5, Callsign: Silverstone, | EAK | AVCODES |
| 6364 | SLR | Los Angeles and Salt Lake R.R. Co. (Salt Lake Route) | 8/1920 | | NAKINA |
| 6365 | SLR | Los Angeles and Salt Lake R.R. Co. (Union Pacific System) | 7/1923-7/1935 | | NAKINA |
| 6366 | SLR | San Pedro, Los Angeles & Salt Lake R.R. (Los Angeles and Salt Lake R.R. Co.) | 8/1920 | | NAKINA |
| 6367 | SLR | St. Lawrence & Atlantic R.R. Co. | added 10/1989; 1/1994-7/2005 | | NAKINA |
| 6368 | SLR | St. Lawrence & Atlantic R.R. Co. | added 10/89; 1/94-7/2000 | | NRHS |
| 6369 | SLR | *SAN PEDRO, LOS ANGELES & SALT LAKE RAILROAD [LOS ANGELES & SALT LAKE RAILROAD CO.} | | | PWRC |
| 6370 | SLR | +ST. LAWRENCE & ATLANTIC RAILROAD COMPANY | | | PWRC |
| 6371 | SLR | St. Lawrence and Atlantic Railroad (Genesee & Wyoming) | | | RSRV |
| 6372 | SLR | St. Lawrence & Atlantic | | CDN | TRAFFIC |
| 6373 | SLRA | SALAS RAMIREZ, LETICIA | | | SCAC4 |
| 6374 | SLRD | Sri Lanka Railway Department | | CL | TRAFFIC |
| 6375 | SLRE | SALINAS ALANIS, RENE | | | SCAC4 |
| 6376 | SLRF | SHOWA LINE, LTD | | | PWRC |
| 6377 | SLRG | San Luis & Rio Grande R.R. Inc. | added 10/2003; 7/2005; eliminated 4/2007 | | NAKINA |
| 6378 | SLRG | SAN LUIS & RIO GRANDE RAILROAD INC. | | | PWRC |
| 6379 | SLRG | San Luis and Rio Grande Railroad | | | RSRV |
| 6380 | SLRG | SAN LUIS & RIO GRANDE RAILROAD INC | | | SCAC4 |
| 6381 | SLRG | San Luis & Rio Grande R.R. Inc. | | USA | TRAFFIC |
| 6382 | SLRJ | SLEIGHT, ROBERT J | | | SCAC4 |
| 6383 | SLRL | SHELL, RUSSELL L | | | SCAC4 |
| 6384 | SLRM | SCORPIO LR TWO (2) POOL LTD | | | SCAC4 |
| 6385 | SLRR | St. Lawrence & Raquette River R.R. | added 7/1990; eliminated 1/1994; 1/1994 (not listed) | | NAKINA |
| 6386 | SLRR | St. Lawrence & Raquette River R.R. | added 7/90; eliminated 1/94 | | NRHS |
| 6387 | SLRR | ST. LAWRENCE & RAQUETTE RIVER RAILROAD | | | PWRC |
| 6388 | SLRR | STEWART-LINER TRANSPORTATION CORP | | | SCAC4 |
| 6389 | SLRS | SMS Rail Service, Inc. | 7/2000-7/2005 | | NAKINA |
| 6390 | SLRS | SMS Rail Service, Inc. | Jul-00 | | NRHS |
| 6391 | SLRS | SMS RAIL SERVICE, INC. | | | PWRC |
| 6392 | SLRS | SMS Rail Service | | | RSRV |
| 6393 | SLRS | SMS RAIL SERVICE INC | | | SCAC4 |
| 6394 | SLRS | SMS Rail Service, Inc. | | USA | TRAFFIC |
| 6395 | SLRU | SILVA LS SP. Z O.O. | | PL | BIC |
| 6396 | SLRU | SHOWA LINE, LTD. | | | PWRC |
| 6397 | SLRU | Showa Line Limited | | | RSRV |
| 6398 | SLRU | SWAN CONTAINER LINE GMBH & CO KG | | | SCAC4 |
| 6399 | SLRW | SKYLINE RAILINGS & WINDOWS INC | | | SCAC4 |
| 6400 | SLRX | St. Louis Refrigerator Car Co. (Manufacturers' Ry. Co.) | 8/1920-7/1923 | | NAKINA |
