| 3101 | ISN | Interisland Airlines | Callsign: Tri-Bird, AOC revoked on 23 April 2010. | RP | AVCODES |
| 3102 | ISN | Interisland Airlines | | | ICAO1 |
| 3103 | ISN | Iowa Southern Utilities Co. | 4/1938 | | NAKINA |
| 3104 | ISN | Iowa Southern Utilities Co. | Apr-38 | | NRHS |
| 3105 | ISN | IOWA SOUTHERN UTILITIES CO. | | | PWRC |
| 3106 | ISNC | I L S INC | | | SCAC4 |
| 3107 | ISNO | ISON OIL COMPANY LLC | | | SCAC4 |
| 3108 | ISNS | IASON SHIPPING LIMITED | | | SCAC4 |
| 3109 | ISOA | I SOURCE TECHNICAL SERVICES INC | | | SCAC4 |
| 3110 | ISOB | ISOBUNKERS LLC | | | SCAC4 |
| 3111 | ISOF | ISLAND OFFSHORE MANAGEMENT AS | | | SCAC4 |
| 3112 | ISOS | ISOM REFRIGERATION LLC | | | SCAC4 |
| 3113 | ISOU | B.O.C. LTD | | | SCAC3 |
| 3114 | ISPC | ISLAND PRECISION MANUFACTURING LTD | | | SCAC4 |
| 3115 | ISPN | ISP | | | SCAC4 |
| 3116 | ISPO | ISPOR | | | SCAC4 |
| 3117 | ISPR | INTERNATIONAL SPECIALTY PRODUCE INC | | | SCAC4 |
| 3118 | ISPT | INDY SPECIALIZED TRANSPORT INC | | | SCAC4 |
| 3119 | ISPV | ITALSEMPIONE SPA | | | SCAC4 |
| 3120 | ISPX | International Specialty Products | 7/2005 (not listed); added 10/2007 | | NAKINA |
| 3121 | ISPX | The Western Company of North America | added 4/1980; eliminated 7/1992; 1/1994 (not listed) | | NAKINA |
| 3122 | ISPX | United States Silica Corp. | added 10/1978; 1/1980; eliminated 1/1980 | | NAKINA |
| 3123 | ISPX | Iron & Steel Products Inc. | 7/1937-1/1946 (not listed); 1/1950; 1/1952-7/1954 (not listed); added 10/1955; eliminated 10/1956 | | NAKINA |
| 3124 | ISPX | Iron & Steel Products Inc. | Jan-52 | | NRHS |
| 3125 | ISPX | United States Silica Corp. | added 10/78; 1/80; eliminated 1/80 | | NRHS |
| 3126 | ISPX | The Western Company of North America | added 4/80; eliminated 7/92; 1/94 | | NRHS |
| 3127 | ISPX | *IRON & STEEL PRODUCTS INC. | | | PWRC |
| 3128 | ISPX | *WESTERN COMPANY OF NORTH AMERICA [UNITED STATES SILICA CORP.] | | | PWRC |
| 3129 | ISPX | +INTERNATIONAL SPECIALTY PRODUCTS | | | PWRC |
| 3130 | ISPX | Western of North America | | | RSRV |
| 3131 | ISPX | INTERNATIONAL SPECIALITY PRODUCTS | | | SCAC4 |
| 3132 | ISPZ | ISU POWER PLANT | | | PWRC |
| 3133 | ISR | Israir Airlines and Tourism Ltd. | IATA: 6H, Callsign: Israir, | IL | AVCODES |
| 3134 | ISR | Israir | IATA: 6H | | ICAO1 |
| 3135 | ISR | Iowa Southern R.R. Co. | added 10/1987; eliminated 4/1990; 1/1994-7/2005 | | NAKINA |
| 3136 | ISR | Iowa Southern R.R. Co. | added 10/87; eliminated 4/90; 1/94-7/2000 | | NRHS |
| 3137 | ISR | IOWA SOUTHERN RAILROAD (CEASED OPERATIONS IN 1989) | | | PWRC |
| 3138 | ISR | Iowa Southern Railroad | | | RSRV |
| 3139 | ISR | IOWA SOUTHERN RAILROAD COMPANY | | | SCAC4 |
| 3140 | ISR | Israel Railways | | IL | VKM |
| 3141 | ISRC | Idaho & Sedalia Transportation Co. LLC | 7/2005 | | NAKINA |
| 3142 | ISRC | IDAHO & SEDALIA TRANSPORTATION CO. LLC | | | PWRC |
| 3143 | ISRC | IDAHO & SEDALIA TRANSPORTATION COMP | | | SCAC4 |
| 3144 | ISRD | ITALIAN STATE RAILROAD | | | SCAC4 |
| 3145 | ISRL | IGLESIAS STELL, RICARDO MANUEL | | | SCAC4 |
| 3146 | ISRN | I S TRAN INC | | | SCAC4 |
| 3147 | ISRP | IOSCO TRANSPORTATION INC | | | SCAC4 |
| 3148 | ISRR | Indiana Southern R.R. Co., Inc. | added 10/1992; eliminated 10/1993; 1/1994 (not listed); added 7/1996; 7/2000-7/2005; eliminated 1/2008 | | NAKINA |
| 3149 | ISRR | Indiana Southern R.R. Co., Inc. | added 10/92; eliminated 10/93; 1/94; added 7/96; 7/2000 | | NRHS |
| 3150 | ISRR | INDIANA SOUTHERN RAILROAD CO. | | | PWRC |
| 3151 | ISRR | Indiana Southern Railroad | | | RSRV |
| 3152 | ISRR | INDIANA SOUTHERN RAILROAD COMPANY I | | | SCAC4 |
| 3153 | ISRR | Indiana Southern Railroad | | USA | TRAFFIC |
| 3154 | ISRT | INTERSTATE US TRANSPORTATION | | | SCAC4 |
| 3155 | ISRU | ISR INVESTMENTS LIMITED | | CY | BIC |
| 3156 | ISRU | ISR INVESTMENT LIMITED | | | SCAC4 |
| 3157 | ISS | Meridiana S.p.A. | IATA: IG, Callsign: Merair, IATA Prefix: 191, Merged with Eurofly S.p.A. | I | AVCODES |
| 3158 | ISS | Alisarda S.p.A. | IATA: IG, Callsign: Alisarda, IATA Prefix: 191, change of name to Meridiana S.p.A. | I | AVCODES |
| 3159 | ISS | Meridiana Fly S.p.A. t/a Meridiana | IATA: IG, Callsign: Meridiana, IATA Prefix: 191, Name changed to Air Italy S.p.A. w.e.f. from 01 Amrch 2018.ICAO designator changed to ISS. Name changed to Meridiana Fly S.p.A. t/a Meridiana. ICAO callsign changed from Merair. Merged with Eurofly S.p.A. | I | AVCODES |
| 3160 | ISS | Air Italy S.p.A. | IATA: IG, Callsign: Air Italy, IATA Prefix: 191, Name changed from Meridiana Fly S.p.A. t/a Meridiana w.e.f. from 01 March 2018.ICAO designator changed to ISS. Name changed to Meridiana Fly S.p.A. t/a Meridiana. ICAO callsign changed from Merair. Merged with Eurofly S.p.A. | I | AVCODES |
| 3161 | ISS | Meridiana | IATA: IG | | ICAO1 |
| 3162 | ISS | ISS Trafficare AB | | SE | VKM |
| 3163 | ISSA | ISSA TRANSPORT SERVICES LLC | | | SCAC4 |
| 3164 | ISSAB | Intercontainer Sweden SUCO AB | | SE | VKM |
| 3165 | ISSD | ITHACA SHIPPING SA | | | SCAC4 |
| 3166 | ISSE | INTEGRITY SERVICES AND SALES INC | | | SCAC4 |
| 3167 | ISSI | INDUSTRIAL SAND SUPPLY INC | | | SCAC4 |
| 3168 | ISSM | ISS-RIOMAR, LLC | | | SCAC4 |
| 3169 | ISSN | ISLAND SERVICE STATION | | | SCAC4 |
| 3170 | ISSQ | INTERNATIONAL SURFACING SYSTEMS INC | | | SCAC4 |
| 3171 | ISSR | ISS Rail, Inc. | added 10/1993; 1/1994-7/2000; eliminated 4/2003; 7/2005 | | NAKINA |
| 3172 | ISSR | ISS Rail, Inc. | added 10/93; 1/94-7/2000 | | NRHS |
| 3173 | ISSR | ISS RAIL, INC. | | | PWRC |
| 3174 | ISSR | ISS Rail | | | RSRV |
| 3175 | ISSS | INCHCAPE SHIPPING SERVICES | | | SCAC4 |
| 3176 | ISSU | AMERICA S TANK CONTAINER SERVICE INC. (ATCOS INC) | | USA | BIC |
| 3177 | ISSU | ICELAND STEAMSHIP CO., LTD. | | | PWRC |
| 3178 | ISSU | Iceland Steamship | | | RSRV |
| 3179 | ISSU | ICELAND STEAMSHIP | | | SCAC1 |
| 3180 | ISSU | ICELAND STEAMSHIP COMPANY, INC. | | | SCAC4 |
| 3181 | ISSW | ITALIA SHIPPING SRL | | | SCAC4 |
| 3182 | ISSX | INTERCHANGE SPECIALTY SERVICE, INC. | | | PWRC |
| 3183 | IST | Istanbul Airlines A.S. | IATA: IL, Callsign: Istanbul, Ceased operations on 25 August 2000. | TR | AVCODES |
| 3184 | IST | Istanbul Airlines | | | ICAO1 |
| 3185 | ISTB | ISLAND TUG AND BARGE LTD | | | SCAC4 |
| 3186 | ISTC | ISLAND TRANSPORTATION CORP | | | SCAC4 |
| 3187 | ISTF | IRON SPRINGS TRANSPORTATION INC | | | SCAC4 |
| 3188 | ISTK | ISLAND TRUCKING | | | SCAC4 |
| 3189 | ISTN | I S TRUCKING | | | SCAC4 |
| 3190 | ISTT | INTERSTATE TRANSPORT INC | | | SCAC4 |
| 3191 | ISTU | 1ST CONTAINERS UK LTD | | GB | BIC |
| 3192 | ISTU | ITC MARITIME SA | | | SCAC4 |
| 3193 | ISTV | IDAHO SPECIALIZED TRANSPORTATION IN | | | SCAC4 |
| 3194 | ISTW | INTERNATIONAL SHIPPING & TRANSPORTA | | | SCAC4 |
| 3195 | ISTX | North American Car Corp. | added 10/1959; 4/1961-1/1975; eliminated 10/1979; 1/1980 | | NAKINA |
| 3196 | ISTX | Interstate Tank Car Corp. | 8/1920-10/1957; eliminated 10/1959 | | NAKINA |
| 3197 | ISTX | North American Car Corp. | added 10/59; 4/61-1/80 | | NRHS |
| 3198 | ISTX | Interstate Tank Car Corp. | 4/38-10/57; eliminated 10/59 | | NRHS |
| 3199 | ISTX | NORTH AMETRICAN CAR CORP. [INTERSTATE TANK CAR CORP.] | | | PWRC |
| 3200 | ISU | Iowa Southern Utilities (Southern Industrial R.R., Inc.) | 1/1975-1/1980 | | NAKINA |
