| 301 | XLOG | XL LOGISTICS AND TRANSPORTATION COR | | | SCAC4 |
| 302 | XLR | Texel Air W.L.L. | Callsign: Texel, IATA Prefix: 565, Founded in 2013. | BRN | AVCODES |
| 303 | XLRT | XLR8 TRUCK LINES | | | SCAC4 |
| 304 | XLS | Excel Aire Service, Inc. | Callsign: Excel Aire, ICAO callsign changed to Excelaire | USA | AVCODES |
| 305 | XLS | ExcelAire, LLC | Callsign: Excelaire, ICAO callsign changed to Excel Aire. Owned by Hawthorne Global Aviation Services, LLC. | USA | AVCODES |
| 306 | XLT | Empresa Brasileira de Infraestrutura | Callsign: Infraero, | BR | AVCODES |
| 307 | XLT | Empressa Brasileira de Infra-Estrutura Aeroportuar | | | ICAO1 |
| 308 | XLTP | XTL LOGISTICS SERVICES INC | | | SCAC4 |
| 309 | XM | Alitalia Express | ICAO: SMX, Callsign: Cee-Cee Express, ICAO callsign changed to Aliexpress | I | AVCODES |
| 310 | XM | Australian Air Express Pty. Ltd. | ICAO: XME, IATA Prefix: 524, Founded in 1992. Commenced operations on 01 August 1992. Merged into Qantas Freight on 06 June 2013. | AUS | AVCODES |
| 311 | XM | Alitalia Express | ICAO: SMX, Callsign: Aliexpress, Designator XM recalled by IATA. ICAO callsign changed from Cee-Cee Express | I | AVCODES |
| 312 | XM | Alitalia Express | ICAO: SMX, Callsign: Aliexpress, w.e.f. from 13 January 2009 assets transferred to new airline C.A.I. First S.p.A. Designator XM reinstated by IATA. ICAO callsign changed from Cee-Cee Express | I | AVCODES |
| 313 | XM | C.A.I. First S.p.A. | ICAO: SMX, w.e.f. 13 January 2009 assets transferred from old airline Alitalia Express. Designator XM reinstated by IATA. ICAO callsign changed from Cee-Cee Express | I | AVCODES |
| 314 | XM | Zimex Aviation Limited | ICAO: IMX, Callsign: Zimex, IATA Prefix: 927, IATA designator changed from C4* | CH | AVCODES |
| 315 | XMA | Martin Aviation Services | | USA | AVCODES |
| 316 | XMA | Martin Aviation Services | | | ICAO1 |
| 317 | XMAT | METROPOLITAN ATLANTA RAPID TRANSIT AUTHORITY (MARTA) | | | PWRC |
| 318 | XMBT | MASSACHUSETTS BAY TRANSIT AUTHORITY | | | PWRC |
| 319 | XMCZ | (MEC) MAINE CENTRAL | | | PWRC |
| 320 | XMCZ | Maine Central Railroad | | | RSRV |
| 321 | XMCZ | MAINE CENTRAL RAILROAD COMPANY | | | SCAC4 |
| 322 | XMDU | XINES LTD | | | SCAC4 |
| 323 | XME | Australian Air Express Pty. Ltd. | IATA: XM, IATA Prefix: 524, Founded in 1992. Commenced operations on 01 August 1992. Merged into Qantas Freight on 06 June 2013. | AUS | AVCODES |
| 324 | XME | Australian air Express | | | ICAO1 |
| 325 | XMG | AMS Group, Joint-Stock Company | | RUS | AVCODES |
| 326 | XMG | AMS Group | | | ICAO1 |
| 327 | XMI | Skyblue Jet Management LLC | Callsign: Zemi, | USA | AVCODES |
| 328 | XMLL | XML LTL | | | SCAC4 |
| 329 | XMOS | M & O SUBWAY | | | PWRC |
| 330 | XMR | Irish Aviation Authority, Flight Check Department | Callsign: Authority, | IRL | AVCODES |
| 331 | XMR | Irish Aviation Authority | | | ICAO1 |
| 332 | XMS | British Airways SANTA | Callsign: Santa, | GB | AVCODES |
| 333 | XMS | British Airways | | | ICAO1 |
| 334 | XMTA | NEW YORK CITY METROPOLITAN TRANSPORTATION AUTHORITY (MTA) | | | PWRC |
| 335 | XMTS | METRO TRANSIT SEATTLE | | | PWRC |
| 336 | XMTZ | XTRA INTERMODAL | | | PWRC |
| 337 | XMTZ | XTRA Intermodal | | | RSRV |
| 338 | XMTZ | XTRA INTERMODAL | | | SCAC4 |
| 339 | XMX | Servicios A La Navegacion En El Espacio Aereo Mexicano (SENEAM) | Callsign: Seneam, | MEX | AVCODES |
| 340 | XMX | SENEAM | | | ICAO1 |
| 341 | XN | Axon Airlines | ICAO: AXO, Callsign: Axonair, IATA Prefix: 304, Suspended operations on 30 November 2001. | GR | AVCODES |
| 342 | XN | Canadian National Telecommunications | ICAO: XNC, Designator XN recalled by IATA. Non-airline Org. in airline industry | CDN | AVCODES |
| 343 | XN | PT. Travel Express Aviation Services d/b/a Xpress Air | ICAO: XAR, Callsign: Travel Express, Name change from PT. Travel Express Aviation Services d/b/a Express Air during 2012. | RI | AVCODES |
| 344 | XN | Fly Logic Malmo AB | Ceased operations on 13 December 2013 due bankrupcy. Formerly Malm� Air Taxi | S | AVCODES |
| 345 | XN | PT. Travel Express Aviation Services d/b/a Express Air | ICAO: XAR, Callsign: Travel Express, Name changed to PT. Travel Express Aviation Services d/b/a xpressair during 2012. | RI | AVCODES |
| 346 | XN | Manasik Aviation Company | ICAO: MNM, Callsign: Manasik, IATA Desigantor changed from MM*. | SA | AVCODES |
| 347 | XNA | Express.Net Airlines | Callsign: Expressnet, | USA | AVCODES |
| 348 | XNA | Express Net Airlines | | | ICAO1 |
| 349 | XNC | Canadian National Telecommunications | Designator XN recalled by IATA. Non-airline Org. in airline industry | CDN | AVCODES |
| 350 | XNC | Canadian National Telecommunications | IATA: XN, Designator XN recalled by IATA. Non-airline Org. in airline industry | CDN | AVCODES |
| 351 | XNC | Canadian National Telecommunications | | | ICAO1 |
| 352 | XNFT | NIAGARA FRONTIER TRANSPORTATION AUTHORITY | | | PWRC |
| 353 | XNPZ | XTRA INTERMODAL | | | SCAC4 |
| 354 | XNR | Taxi Aereo del Norte, S.A. de C.V. | Callsign: Taxi Norte, | MEX | AVCODES |
| 355 | XNR | Taxi Aero Del Norte | | | ICAO1 |
| 356 | XNS | Navtech System Support, Inc. | | CDN | AVCODES |
| 357 | XNS | Navtech System Support | | | ICAO1 |
| 358 | XNT | Notams International, Inc. | Non-airline Org. in airline industry | USA | AVCODES |
| 359 | XNT | Notams International | | | ICAO1 |
| 360 | XNV | Tigin Ltd. d/b/a Navinc Airlines Services | | USA | AVCODES |
| 361 | XNV | Navinc Airlines Services | | | ICAO1 |
| 362 | XNWZ | NORFOLK SOUTHERN RAILWAY COMPANY | | | PWRC |
| 363 | XNWZ | Norfolk Southern Railway | | | RSRV |
| 364 | XNWZ | NORFOLK SOUTHERN RAILWAY COMPANY (N | | | SCAC4 |
| 365 | XO | LTE International Airways S.A. | ICAO: LTE, Callsign: Fun Jet, Established on 29 April 1987. Commenced operations on 01 November 1987. Ceased operations on 17 October 2008. Name changed to Volar Airlines w.e.f. 24 May 2001. Name reverted back to LTE International Airways S.A. during 2005. | E | AVCODES |
| 366 | XO | China Xinjiang Airlines | ICAO: CXJ, Callsign: Xinjiang, Designator XO* recalled by IATA. Name changed from Zinjiang Airlines | PRC | AVCODES |
| 367 | XO | Xinjiang Airlines | ICAO: CXJ, Callsign: Xinjiang, Name changed to ChinaZinjiang Airlines | PRC | AVCODES |
| 368 | XO | South East Asian Airlines (Seair) International, Inc. | ICAO: SGD, Callsign: Air Blue, IATA Prefix: 397, | RP | AVCODES |
| 369 | XOJ | PCMT Aviation/Xoket, Inc. | Callsign: Xojet, Name changed to Xojet, Inc. | USA | AVCODES |
| 370 | XOJ | Xojet, Inc. | Callsign: Xojet, ICAO callsign changed to Exojet. Name changed from PCMT Aviation/Xoket, Inc. | USA | AVCODES |
| 371 | XOJ | Xojet, Inc. | Callsign: Exojet, Name changed to Xojet Aviation LLC. ICAO callsign changed from Xojet. Name changed from PCMT Aviation/Xoket, Inc. | USA | AVCODES |
| 372 | XOJ | Xojet Aviation LLC | Callsign: Exojet, Name changed from Xojet, Inc. ICAO callsign changed from Xojet. Name changed from PCMT Aviation/Xoket, Inc. | USA | AVCODES |
| 373 | XOLO | X ONE (X1) LOGISTICS | | | SCAC4 |
| 374 | XOMU | EXXONMOBIL CORPORATION | | USA | BIC |
| 375 | XOMX | Exxon Mobil Corp. | added 7/2000; 7/2000-7/2005 | | NAKINA |
| 376 | XOMX | Exxon Mobil Corp. | added 7/2000; 7/2000 | | NRHS |
| 377 | XOMX | EXXON-MOBIL CORPORATION | | | PWRC |
| 378 | XOMX | Exxon-Mobil Corporation | | | RSRV |
| 379 | XOMX | EXXON MOBIL CORPORATION | | | SCAC4 |
| 380 | XONE | XPRESS NETWORK SOLUTIONS (A DIVISIO | | | SCAC4 |
| 381 | XOOZ | FLEXI-VAN LEASING INC | | | SCAC4 |
| 382 | XOXU | BULK CONTAINER GROUP LLC | | USA | BIC |
| 383 | XP | T.E.M. Enterprises Inc. d/b/a Casino Express | ICAO: CXP, Callsign: Casino Express, Name changed to T.E.M. Enterprises Inc. d/b/a Xtra Airways. Founded in 1987. | USA | AVCODES |
| 384 | XP | DHL Aero Express, S.A. | ICAO: DAE, IAATA changed to DS | PA | AVCODES |
| 385 | XP | Avior Airlines Pty Ltd. | | AUS | AVCODES |
| 386 | XP | T.E.M. Enterprises Inc. d/b/a Xtra Airways | ICAO: CXP, Callsign: Ruby Mountain, Naem changed to T.E.M. Enterprises Inc. d/b/a Avelo Airlines. ICAO designator changed to VXP. Accounting code 615 recalled by IATA. Founded in 1987. Name changed from T.E.M. Enterprises Inc. d/b/a Casino Express | USA | AVCODES |
| 387 | XP | T.E.M. Enterprises Inc. d/b/a Avelo Airlines | ICAO: CXP, Callsign: Avelo, Name chanaged to T.E.M. Enterprises Inc. d/b/a Xtra Airways. ICAO designator changed to VXP. Founded in 1987. Name changed from T.E.M. Enterprises Inc. d/b/a Xtra Airways and previously T.E.M. Enterprises Inc. d/b/a Casino Express | USA | AVCODES |
| 388 | XP | T.E.M. Enterprises Inc. d/b/a Avelo Airlines | ICAO: VXP, Callsign: Avelo, Name chanaged to T.E.M. Enterprises Inc. d/b/a Xtra Airways. ICAO designator changed from CXP. Founded in 1987. Name changed from T.E.M. Enterprises Inc. d/b/a Xtra Airways and previously T.E.M. Enterprises Inc. d/b/a Casino Express | USA | AVCODES |
| 389 | XP | Xaver Pittrrich Bauunternehmung GmbH = Co KO | | DE | VKM |
| 390 | XPA | Pan Am Weather Systems | | USA | AVCODES |
| 391 | XPA | Pan Am Weather Systems | | | ICAO1 |
| 392 | XPAH | PORT AUTHORITY TRANS HUDSON (PATH, NY-NJ) | | | PWRC |
| 393 | XPAL | PORT AUTHORITY TRANSIT CORP. (PHILADELPHIA AREA) - LINDENWOLD NJ LINE | | | PWRC |
| 394 | XPAT | PORT AUTHORITY TRANSIT (PITTSBURGH - ALLEGHENY COUNTY) | | | PWRC |
| 395 | XPAU | EXPANSION SAS | | F | BIC |
| 396 | XPAU | EXPANSION SAS | | | SCAC4 |
| 397 | XPCU | SMA SOLAR TECHNOLOGY AG | | D | BIC |
| 398 | XPD | Expedition Airways | Callsign: Expedition, Designator FO* recalled by IATA | ZW | AVCODES |
| 399 | XPD | Expedition Airways | IATA: FO, Callsign: Expedition, Designator FO* recalled by IATA | ZW | AVCODES |
| 400 | XPDS | XPURT INDUSTRIAL COURIERS | | | SCAC4 |
