| 5901 | SKWO | STREETHAWK TOWING SERVICES INC | | | SCAC4 |
| 5902 | SKWS | S & K WATER TRUCK SERVICE CO | | | SCAC4 |
| 5903 | SKWY | SKYWAY DELIVERY | | | SCAC4 |
| 5904 | SKX | Skyways Express AB | IATA: JZ, Callsign: Sky Express, IATA Prefix: 752, Ceased Operations and filed for Bankrupcy on 12 May 2012. Name changed to Avia Express Sweden AB. Name changed from Skyways AB | S | AVCODES |
| 5905 | SKX | Skyways AB | IATA: JZ, Callsign: Sky Express, IATA Prefix: 752, Name changed to Skyways Express AB | S | AVCODES |
| 5906 | SKX | Salair AB | Callsign: Sky Express, Name changed to Skyways AB. Name changed from AMA-Flyg I Goteborg HB. ICAO designator changed from AAX | S | AVCODES |
| 5907 | SKX | Avia Express Sweden AB | IATA: JZ, IATA Prefix: 752, Ceased operations on 22 May 2012. Name changed from Skyways Express AB w.e.f. 01 December 2010. Name changed to Skyways AB | S | AVCODES |
| 5908 | SKX | Alliance Air Company LLC | Callsign: Skystorm, | AM | AVCODES |
| 5909 | SKX | Sky Airline Peru S.A.C. | IATA: H8, Callsign: Sky Peru, | PE | AVCODES |
| 5910 | SKX | Skyways Express | IATA: JZ | | ICAO1 |
| 5911 | SKX | Spencer Kellogg & Sons, Inc. | 8/1920-1/1943 | | NAKINA |
| 5912 | SKX | General American Transportation Corp. | 1/1945-4/1947 | | NAKINA |
| 5913 | SKX | Spencer Kellogg & Sons, Inc. | Apr-38 | | NRHS |
| 5914 | SKX | *SPENCER KELLOGG & SONS, INC. | | | PWRC |
| 5915 | SKX | *GENERAL AMERICAN TRANSPORTATION CORP. | | | PWRC |
| 5916 | SKXE | SKIPPER XPRESS | | | SCAC4 |
| 5917 | SKXG | STARMARK TRANSPORT INC | | | SCAC4 |
| 5918 | SKXH | SKYLINE TRANSPORTING SERVICES LLC | | | SCAC4 |
| 5919 | SKXI | SHOCK TRANSPORT INC | | | SCAC4 |
| 5920 | SKXL | SOKIL EXPRESS LINES LTD | | | SCAC4 |
| 5921 | SKXM | SPIKE EXPRESS LLC | | | SCAC4 |
| 5922 | SKXN | SKEETER EXPRESS INC | | | SCAC4 |
| 5923 | SKXS | SKYLINE EXPRESS INC | | | SCAC4 |
| 5924 | SKXT | SKURSKI TRANSPORT INC | | | SCAC4 |
| 5925 | SKXV | S & K TRANSPORTATION SERVICES LLC | | | SCAC4 |
| 5926 | SKY | Skymark Airlines Co. Ltd. | IATA: BC, Callsign: Skymark, Designator BC reinstated by IATA | J | AVCODES |
| 5927 | SKY | Cooper Skybird Air Charters Ltd. | | EAK | AVCODES |
| 5928 | SKY | Skymark Airlines | IATA: BC | | ICAO1 |
| 5929 | SKY | Skymark Airlines | | J | TRAFFIC |
| 5930 | SKYA | SKYLINE TRANSPORT INC | | | SCAC4 |
| 5931 | SKYB | SKYWALKE | | | SCAC4 |
| 5932 | SKYBUS | SkyBus | | AUS | TRAFFIC |
| 5933 | SKYC | SKYLINE COVER LLC | | | SCAC4 |
| 5934 | SKYD | SPARKS, CORY M | | | SCAC4 |
| 5935 | SKYE | SKYLANDS ENERGY SERVICE INC | | | SCAC4 |
| 5936 | SKYH | SKYWARD INTERNATIONAL INC | | | SCAC4 |
| 5937 | SKYI | SKYE TRUCKING COMPANY | | | SCAC4 |
| 5938 | SKYK | SKYLARK VAN SERVICE INC | | | SCAC4 |
| 5939 | SKYM | SKYLINE MESSENGER SERVICE INC | | | SCAC4 |
| 5940 | SKYP | SKY-LINC SYSTEMS INC | | | SCAC4 |
| 5941 | SKYR | SVK TRANSPORT LLC | | | SCAC4 |
| 5942 | SKYS | SKYLINE POTATO COMPANY | | | SCAC4 |
| 5943 | SKYSS | Skyss (Vestland county) | | N | TRAFFIC |
| 5944 | SKYT | SKYLINE TRANSPORTATION, INC | | | SCAC1 |
| 5945 | SKYT | SKYLINE TRANSPORTATION, INC | | | SCAC4 |
| 5946 | SKYTR | SkyTrain | City: Vancouver | CDN | TRAFFIC |
| 5947 | SKYU | CAI INTERNATIONAL | | USA | BIC |
| 5948 | SKYU | CAI International | | | RSRV |
| 5949 | SKYU | CONTAINER APPLICATIONS INTERNATIONA | | | SCAC4 |
| 5950 | SKYV | SKYVIEW FARMS INC | | | SCAC4 |
| 5951 | SKYW | SKYWAY TRANSPORTATION INC | | | SCAC4 |
| 5952 | SKYWAYS | | | | TRAFFIC |
| 5953 | SKYX | Nortex Refining Co. | 8/1920 | | NAKINA |
| 5954 | SKYX | Skelly Oil Co. — series 10 and 15, 1001 to 1010 | 8/1920 | | NAKINA |
| 5955 | SKYX | Skelly Oil Co. | 7/1923-7/1932 | | NAKINA |
| 5956 | SKYX | Skelly Oil Co. (Union Tank Car Co.) | 7/1935 | | NAKINA |
| 5957 | SKYX | Union Tank Car Co. | 7/1937 (not listed) | | NAKINA |
| 5958 | SKYX | SKELLY OIL CO. [NORTEX REFINING CO.] (UNION TANK CAR CO.) | | | PWRC |
| 5959 | SKZ | Skyway Enterprises, Inc. | IATA: KI, Callsign: Skyway-Inc, Designator KI* recalled by IATA. Designator KI* reinstated by IATA | USA | AVCODES |
| 5960 | SKZ | Skyway Enterprises | | | ICAO1 |
| 5961 | SKZ | SPENCER KELLOGG | | | PWRC |
| 5962 | SKZI | STI | | | SCAC4 |
| 5963 | SKZL | SKYS THE LIMIT TRUCKING LLC | | | SCAC4 |
| 5964 | SKZN | STEALTH TRUCKLINES INC | | | SCAC4 |
| 5965 | SKZT | SHENK TRANSPORT | | | SCAC4 |
| 5966 | SL | Rio Sul Linhas Aereos, S.A. | ICAO: RSL, Callsign: Riossul, IATA Prefix: 293, Merged with Nordeste and then into Varig. Name changed from Rio-Sul Servicos Aereos Regionais, S.A. Designator SL reinstated by IATA | BR | AVCODES |
| 5967 | SL | Rio-Sul Servicos Aereos Regionais, S.A. | ICAO: RSL, Callsign: Riossul, IATA Prefix: 293, Name changed to Rio Sul Linhas Aereas S.A. Designator SL reinstated by IATA | BR | AVCODES |
| 5968 | SL | Southeast Airlines, Inc. | ICAO: SNK, Callsign: Southeast, Commenced operations in 1999. Ceased operations on 30 November 2004 | USA | AVCODES |
| 5969 | SL | Caribbean Skyways St. Lucia Express | ICAO: CSC, Callsign: St. Lucia Express, | WL | AVCODES |
| 5970 | SL | Air Sylhet AG | ICAO: SHR, Founded in 2007. Commenced operations on 04 April 2009. Ceased operations operations in May 2009. | A | AVCODES |
| 5971 | SL | Air Atlantic Sarl | ICAO: AIA, | P | AVCODES |
| 5972 | SL | Thai Lion Mentari Co. Ltd. | ICAO: TLM, Callsign: Mentari, | T | AVCODES |
| 5973 | SL | Scandinavian Airlines Ireland Limited | ICAO: SZS, Callsign: Spinnaker, Name changed to Scandinavian Airlines Ireland Limited d/b/a SAS Connect w.e.f. 28 September 2021. | IRL | AVCODES |
| 5974 | SL | Scandinavian Airlines Ireland Limited d/b/a SAS Connect | ICAO: SZS, Callsign: Spinnaker, Name changed from Scandinavian Airlines Ireland Limited w.e.f. 28 September 2021. | IRL | AVCODES |
| 5975 | SL | Sugar Land Ry. | 4/1938-7/1954 | | NAKINA |
| 5976 | SL | Salt Lake City Southern R.R. Co., Inc. | 1/1994-7/2005 | | NAKINA |
| 5977 | SL | Sugar Land Ry. | 4/38-1/52 | | NRHS |
| 5978 | SL | Salt Lake City Southern R.R. Co., Inc. | 1/94-7/2000 | | NRHS |
| 5979 | SL | *SUGAR LAND RWY. | | | PWRC |
| 5980 | SL | +SALT LAKE CITY SOUTHERN RAILROAD COMPANY, INC. | | | PWRC |
| 5981 | SL | Salt Lake City Southern Railroad | | | RSRV |
| 5982 | SL | SALT LAKE CITY SOUTHERN RAILROAD CO | | | SCAC4 |
| 5983 | SL | Storstockholms Lokaltrafiks | Real: SS, City: Stockholm | S | TRAFFIC |
| 5984 | SL | Storstockhoms Lokaltrafik | | SE | VKM |
| 5985 | SL&E | Sligo & Eastern R.R. | 7/1923 | | NAKINA |
| 5986 | SL&E | SLIGO & EASTERN RAILROAD | | | PWRC |
| 5987 | SL&H | St. Louis & Hannibal R.R. Co. | 7/1923-4/1938 | | NAKINA |
| 5988 | SL&H | St. Louis & Hannibal R.R. Co. | Apr-38 | | NRHS |
| 5989 | SL&H | ST. LOUIS & HANNIBAL RAILROAD CO. | | | PWRC |
| 5990 | SL&L | Salt Lake, Garfield & Western Ry. Co. | 4/1938 | | NAKINA |
| 5991 | SL&L | Salt Lake, Garfield & Western Ry. Co. | Apr-38 | | NRHS |
| 5992 | SL&L | SALT LAKE, GARFIELD & WESTERN RWY. CO. | | | PWRC |
| 5993 | SL&U | Salt Lake & Utah R.R. Co. | 7/1923-7/1936 | | NAKINA |
| 5994 | SL&U | SATL LAKE & UTAH RAILROAD CO. | | | PWRC |
| 5995 | SLA | Sierra National Airlines | IATA: LJ, Callsign: Selair, IATA Prefix: 690, Designator LJ recalled by IATA | WAL | AVCODES |
| 5996 | SLA | Sierra National Airlines | IATA: LJ | | ICAO1 |
| 5997 | SLAB | SCIERIE LABRANCHE INC | | | SCAC4 |
| 5998 | SLAC | ST LAWRENCE AND ATLANTIC (QUEBEC) R | | | SCAC4 |
| 5999 | SLAF | Sri Lanka Air Force | | CL | TRAFFIC |
| 6000 | SLAG | STATELINE AG SERVICE INC | | | SCAC4 |
