| 6001 | SLAL | South Plains Lamesa R.R., Ltd. | 7/2000-7/2005 | | NAKINA |
| 6002 | SLAL | South Plains Lamesa R.R., Ltd. | Jul-00 | | NRHS |
| 6003 | SLAL | SOUTH PLAINS LAMESA RAILROAD, LTD. | | | PWRC |
| 6004 | SLAL | South Plains Lamesa Railroad | | | RSRV |
| 6005 | SLAL | SOUTH PLAINS LAMESA RAILROAD LTD | | | SCAC4 |
| 6006 | SLAN | | City: Slanska Ruda | PL | TRAFFIC |
| 6007 | SLANC | South Lancs Travel | | GB | TRAFFIC |
| 6008 | SLAO | S.L.A. TRANSPORT, INC | | | SCAC1 |
| 6009 | SLAQ | SALT EXCHANGE | | | SCAC4 |
| 6010 | SLAR | STELLAR FREIGHT LIMITED | | | SCAC1 |
| 6011 | SLAR | STELLAR LINES S A | | | SCAC4 |
| 6012 | SLAS | SUNSPROUTS OF LANCASTER COUNTY | | | SCAC4 |
| 6013 | SLAT | SALLEE EXPRESS | | | SCAC4 |
| 6014 | SLAW | St. Lawrence R.R., Division of National Railway Utilization Corp. | 1/1980 | | NAKINA |
| 6015 | SLAW | St. Lawrence R.R. | eliminated 7/1990 | | NAKINA |
| 6016 | SLAW | St. Lawrence R.R., Division of National Railway Utilization Corp. | Jan-80 | | NRHS |
| 6017 | SLAW | St. Lawrence R.R. | eliminated 7/90 | | NRHS |
| 6018 | SLAW | ST. LAWRENCE RAILROAD, DIV. NATIONAL RAILWAY UTILIZATION CORP. | | | PWRC |
| 6019 | SLAW | St. Lawrence Railroad | | | RSRV |
| 6020 | SLAW | SECURITY LOGISTICS LLC | | | SCAC4 |
| 6021 | SLAX | St. Lawrence Starch Co. Ltd. | 7/1937-1/1980; eliminated 10/1987 | | NAKINA |
| 6022 | SLAX | St. Lawrence Starch Co. Ltd. | 4/38-1/80; eliminated 10/87 | | NRHS |
| 6023 | SLAX | ST. LAWRENCE STARCH CO., LTD. | | | PWRC |
| 6024 | SLAX | St. Lawrence Starch | | | RSRV |
| 6025 | SLAY | SLAY TRANSPORTATION CO | | | SCAC1 |
| 6026 | SLAY | SLAY TRANSPORTATION CO INC | | | SCAC4 |
| 6027 | SLAZ | SLA PROPERTY MANAGEMENT LIMITED PARTNERSHIP | | | PWRC |
| 6028 | SLB | Slok Air Limited | Callsign: Slok Air, | WAN | AVCODES |
| 6029 | SLB | Slok Air | | | ICAO1 |
| 6030 | SLB | Salzburger Lokalbahn | | A | TRAFFIC |
| 6031 | SLB | Salzburg AG für Energie, Verkehr und Telekommunikation - Salzburger Lokalbahn | | AT | VKM |
| 6032 | SLBB | SHOWA LINE, LTD. | | | PWRC |
| 6033 | SLBF | STORAGE SOLUTIONS | | | SCAC4 |
| 6034 | SLBI | SCL BASILEA AG | | | SCAC4 |
| 6035 | SLBK | SHOWA LINE, LTD. | | | PWRC |
| 6036 | SLBL | SLOTLABEL INC | | | SCAC4 |
| 6037 | SLBN | STRATTON LUMBER INC | | | SCAC4 |
| 6038 | SLBO | SCHUTTE LUMBER COMPANY | | | SCAC4 |
| 6039 | SLBQ | SELDEN TRUCKING INC | | | SCAC4 |
| 6040 | SLBT | SILVER BULLET TRUCKING | | | SCAC4 |
| 6041 | SLBU | SHOWA LINE, LTD. | | | PWRC |
| 6042 | SLBU | Showa Line Limited | | | RSRV |
| 6043 | SLBV | STERLING HELICOPTER | | | SCAC4 |
| 6044 | SLBY | S L B TRANSIT INC | | | SCAC4 |
| 6045 | SLC | Swiftlines Limited | Callsign: Swiftlines, | EAK | AVCODES |
| 6046 | SLC | Salsa D'Haiti | IATA: SO, Ceased operations | RH | AVCODES |
| 6047 | SLC | San Luis Central R.R. | 1/1941-7/1954 | | NAKINA |
| 6048 | SLC | The San Luis Central R.R. Co. | 1/1975-7/2005 | | NAKINA |
| 6049 | SLC | San Luis Central R.R. | Jan-52 | | NRHS |
| 6050 | SLC | The San Luis Central R.R. Co. | 1/75-7/2000 | | NRHS |
| 6051 | SLC | SAN LUIS CENTRAL RAILROAD CO. | | | PWRC |
| 6052 | SLC | San Luis Central Railroad | | | RSRV |
| 6053 | SLC | San Luis Central R.R. | | USA | TRAFFIC |
| 6054 | SLCA | S & L CARRIERS INC | | | SCAC4 |
| 6055 | SLCB | SELECTIVE DISTRIBUTION LLC | | | SCAC4 |
| 6056 | SLCD | SCHNEIDER LOGISTICS INC (INTEGRATED | | | SCAC4 |
| 6057 | SLCF | SHOWA LINE, LTD. | | | PWRC |
| 6058 | SLCF | SPEED LIGHT COURIER & LTL CO INC | | | SCAC4 |
| 6059 | SLCF | SALCEF S.p.A. | | IT | VKM |
| 6060 | SLCP | SEA LAUNCH COMPANY LLC | | | SCAC4 |
| 6061 | SLCR | ST. LOUIS & CHAIN OF ROCKS RAILROAD | | | PWRC |
| 6062 | SLCT | SEALAND CONSTRUCTION LTEE | | | SCAC4 |
| 6063 | SLCU | SPECTRA TANKTAINER LOGISTICS PTE. LTD | | SGP | BIC |
| 6064 | SLCU | *SALT LAKE CITY UNION DEPOT & RAILWAY CO. | | | PWRC |
| 6065 | SLCU | *SLC SOCIETE LOCATION CONTAINERS | | | PWRC |
| 6066 | SLCU | SLC Societe Location Containers | | | RSRV |
| 6067 | SLCU | CONTAINER ASSOCIATION ROTTERDAM BV | | | SCAC4 |
| 6068 | SLCW | SLC NATIONWIDE INC | | | SCAC4 |
| 6069 | SLCX | *ST. LAWRENCE COUNTY INDUSTRIAL DEVELOPMENT AGENCY | | | PWRC |
| 6070 | SLCX | +ST. LAWRENCE CEMENT INC. | | | PWRC |
| 6071 | SLCX | ST LAWRENCE CEMENT INC | | | SCAC4 |
| 6072 | SLCY | SCHNEIDER LOGISTICS INC (ALLIANCE C | | | SCAC4 |
| 6073 | SLCZ | SEABOARD LUMBER CO. | | | PWRC |
| 6074 | SLD | Silver Air spol. s.r.o. | Callsign: Solid, | CZ | AVCODES |
| 6075 | SLD | Silver Air | | | ICAO1 |
| 6076 | SLDC | SST LEASING LLC | | | SCAC4 |
| 6077 | SLDD | SOUTHLAND TRANSPORTATION COMPANY | | | SCAC4 |
| 6078 | SLDE | SOUTHLAND EXPRESS, INC | | | SCAC1 |
| 6079 | SLDE | SOUTHLAND EXPRESS INC | | | SCAC4 |
| 6080 | SLDG | STIMMELL, DAVID TRUCKING LLC | | | SCAC4 |
| 6081 | SLDN | SHELDON TRANSPORTATION CO | | | SCAC1 |
| 6082 | SLDO | SALGADO, SERGIO | | | SCAC4 |
| 6083 | SLDQ | STL XPRESS | | | SCAC4 |
| 6084 | SLDR | SHOWA LINE, LTD. | | | PWRC |
| 6085 | SLDS | SCHNEIDER LOGISTICS TRANSLOADING AN | | | SCAC4 |
| 6086 | SLDT | SOUTHLAND TRUCK LINE INC | | | SCAC4 |
| 6087 | SLDU | SHOWA LINE, LTD. | | | PWRC |
| 6088 | SLDU | Showa Line Limited | | | RSRV |
| 6089 | SLDV | SLD TRANSPORT INC | | | SCAC4 |
| 6090 | SLE | Streamline CC | Callsign: Slipstream, | ZA | AVCODES |
| 6091 | SLE | Streamline | | | ICAO1 |
| 6092 | SLEB | SEATTLE-TACOMA BOX CO | | | SCAC4 |
| 6093 | SLEC | SMALLEY TRUCKING CO INC | | | SCAC4 |
| 6094 | SLEF | SUNLINE EXPRESS SYSTEMS, INC | | | SCAC1 |
| 6095 | SLEF | SUNLINE EXPRESS SYSTEMS INC | | | SCAC4 |
| 6096 | SLEH | SNOWLAND FREIGHT SERVICES INC | | | SCAC4 |
| 6097 | SLEI | STAGELINE EXPRESS INC | | | SCAC4 |
| 6098 | SLEM | SALEM, H R TRANSPORT LLC | | | SCAC4 |
| 6099 | SLEN | SEALMASTER ALLENTOWN | | | SCAC4 |
| 6100 | SLEO | STRAIGHT LINE EXPRESS INC | | | SCAC4 |
