| 1 | AO | Aviacion Y Comercial S.A. (Aviaco) | ICAO: AYC, Callsign: Aviaco, Merged into Iberia w.e.f. 01 September 1999. | E | AVCODES |
| 2 | AO | Australian Airlines Ltd. | ICAO: AUZ, Callsign: Australian, Established in 2001. Commenced operations on 27 October 2002. Ceased operations on 30 June 2006. Low cost subsidiary of Qantas | AUS | AVCODES |
| 3 | AO | Avianova LCC | ICAO: VNV, Commenced operations on 27 August 2009. Ceased Operations on 09 October 2011. | RUS | AVCODES |
| 4 | AO | Air One Aviation Pvt Ltd d/b/a Air One Aviation | IATA Prefix: 970, Designator AO recalled by IATA. | IND | AVCODES |
| 5 | AO | Air Juan Aviation, Inc. | | RP | AVCODES |
| 6 | AO | Appalachian & Ohio R.R. Inc. | 7/2005 | | NAKINA |
| 7 | AO | *ADIRONDACK ORE MINES (REPUBLIC STEEL) | | | PWRC |
| 8 | AO | +APPALACHIAN & OHIO RAILROAD INC. | | | PWRC |
| 9 | AO | Appalachian and Ohio Railroad | | | RSRV |
| 10 | AO | APPALACHIAN & OHIO RAILROAD INC | | | SCAC4 |
| 11 | AO&M | ASHLAND ODANAH & MARENGO RAILWAY | | | PWRC |
| 12 | AOA | Alcon Servicios Aereos, S.A. de C.V. | Callsign: Alcon, | MEX | AVCODES |
| 13 | AOA | Apollo Airlines, S.A. | IATA: PJ, Callsign: Apollo Air, Ceased operations during 1997. | GR | AVCODES |
| 14 | AOA | Apollo Airlines, S.A. | IATA: K6, Callsign: Apollo Air, IATA designator changed from PJ | GR | AVCODES |
| 15 | AOA | Air Ocean Airlines LLC | Callsign: Air Ocean, | UA | AVCODES |
| 16 | AOA | Alcon Servicios Aereos, S.A. de C.V. | | | ICAO1 |
| 17 | AOAB | A-ONE (A-1) ABC AUTO DRIVE AWAY | | | SCAC3 |
| 18 | AOAD | ASTRAL OCEANICA ARMADORA SA | | | SCAC3 |
| 19 | AOAD | ARROW WRECKER SERVICE INC | | | SCAC4 |
| 20 | AOAE | AUTO AIR SERVICES | | | SCAC3 |
| 21 | AOAE | AUSTROMAR OBCHODNI A DOPRAVNI SPOL | | | SCAC4 |
| 22 | AOAH | ASTRIDGE INTERNATIONAL | | | SCAC4 |
| 23 | AOAI | ARMSTRONG RELOCATION | | | SCAC4 |
| 24 | AOAJ | AMITE OIL CO LLC | | | SCAC4 |
| 25 | AOAK | ADEN OF AVON INC | | | SCAC4 |
| 26 | AOAL | A-ONE (A-1) CO OF CLARKSVILLE INC | | | SCAC4 |
| 27 | AOAM | A-ONE (A-1) ALLSTATE MOVERS INC | | | SCAC3 |
| 28 | AOAN | A-ONE (A-1) ADVENTURE TRAVEL INC | | | SCAC3 |
| 29 | AOAN | A ONE (A1) LOGISTICS LLC | | | SCAC4 |
| 30 | AOAO | A-ONE (A-1) ACE MOVING & STORAGE OF | | | SCAC3 |
| 31 | AOAO | AOL SOLUTIONS INC | | | SCAC4 |
| 32 | AOAP | AOA TRANSPORT | | | SCAC3 |
| 33 | AOAP | ARMSTRONG RELOCATION NASHVILLE TENN | | | SCAC4 |
| 34 | AOAQ | A-ONE (A-1) FAMILY TOWING INC | | | SCAC4 |
| 35 | AOAR | A-ONE (A-1) RELOCATION INCORPORATED | | | SCAC3 |
| 36 | AOAR | A-ONE (A-1) LOGISTICS INC | | | SCAC4 |
| 37 | AOAS | AI TRANSPORT CO | | | SCAC4 |
| 38 | AOAT | ACTION TRUCKING LLC | | | SCAC4 |
| 39 | AOAV | A-ONE (A-1) AUTO MOVERS | | | SCAC3 |
| 40 | AOAW | ALDERMAN OIL COMPANY | | | SCAC4 |
| 41 | AOB | Aerocaribe Cord, С.А. | Callsign: ???ib? Cord, | YV | AVCODES |
| 42 | AOB | Autobus Oberbayern GmbH | | D | TRAFFIC |
| 43 | AOBF | AUTO-BON FORWARDING INC | | | SCAC3 |
| 44 | AOBF | A-ONE (A-1) MOVING & STORAGE INC | | | SCAC4 |
| 45 | AOBG | ACROBAG | | | SCAC4 |
| 46 | AOBK | ABJ LOGISTICS INC | | | SCAC4 |
| 47 | AOBL | A-ONE (A-1) BUS LINES INC | | | SCAC3 |
| 48 | AOBM | ARNOLD, BILLY M INC | | | SCAC3 |
| 49 | AOBN | ARMSTRONG RELOCATION (BROKERAGE DVI | | | SCAC4 |
| 50 | AOBO | ATLANTIC OBO TRANSPORTERS LTD. | | | SCAC3 |
| 51 | AOBP | AUTOBUS PONTIAC TOURS SOL AIR MER I | | | SCAC3 |
| 52 | AOBP | A-ONE (A-1) INTERMODAL INC | | | SCAC4 |
| 53 | AOBS | AUTO-PRO TRANSPORT INC | | | SCAC3 |
| 54 | AOBS | ALDI TRANSFER | | | SCAC4 |
| 55 | AOBT | ALTON, BARBARA TRUCKING | | | SCAC3 |
| 56 | AOC | TitanFly International S.r.l. | Callsign: Aramis, Name changed to Air Eclipse International S.r.l. | RSM | AVCODES |
| 57 | AOC | Air Eclipse International S.r.l. | Callsign: Aramis, Name changed from TitanFly International S.r.l. | RSM | AVCODES |
| 58 | AOC | AVCOM | IATA: J6 | | ICAO1 |
| 59 | AOCA | ARCO COAL SALES COMPANY | | | SCAC3 |
| 60 | AOCA | AINSLEY OIL COMPANY INC | | | SCAC4 |
| 61 | AOCB | A-ONE (A-1) CHARTERS INC | | | SCAC3 |
| 62 | AOCB | ALVES OIL CO INC | | | SCAC4 |
| 63 | AOCC | A-ONE (A-1) CITY CAB SHUTTLE CORPOR | | | SCAC3 |
| 64 | AOCD | AMADOR COMPANIA ARMADORA S A | | | SCAC3 |
| 65 | AOCD | AOC MEXICO SA DE CV | | | SCAC4 |
| 66 | AOCE | A-ONE (A-1) CHICAGO COURIER INC | | | SCAC3 |
| 67 | AOCF | AMERICAN OCEAN FREIGHT SERVICES INC | | | SCAC3 |
| 68 | AOCG | ASTRO CARTAGE INC | | | SCAC3 |
| 69 | AOCG | ASTRO CARTAGE INC | | | SCAC4 |
| 70 | AOCH | A ONE CARRIERS INC | | | SCAC4 |
| 71 | AOCI | A-ONE (A-1) COURIER | | | SCAC3 |
| 72 | AOCI | AARON OIL COMPANY INC | | | SCAC4 |
| 73 | AOCK | AIR OCEAN CARGO USA LLC | | | SCAC4 |
| 74 | AOCL | AMERICAN OCEAN LINES | | | SCAC3 |
| 75 | AOCL | ALTO CONTAINER LINE INC | | | SCAC4 |
| 76 | AOCM | A-ONE (A-1) CARRIER MOVING & STORAG | | | SCAC3 |
| 77 | AOCN | AIRPORT CONNECTION INC, THE, | | | SCAC3 |
| 78 | AOCN | A ONE (A1) CARGO CORPORATION | | | SCAC4 |
| 79 | AOCO | AERO CHARTERS & TOURS | | | SCAC3 |
| 80 | AOCP | ASTRA COMPANIA ARGENTINA DE PETROLE | | | SCAC3 |
| 81 | AOCP | AAA OIL CO-PRIESTLEY HEATING OIL | | | SCAC4 |
| 82 | AOCQ | ASHFORD, T P OIL COMPANY | | | SCAC3 |
| 83 | AOCR | ARMOR CARRIERS INC | | | SCAC3 |
| 84 | AOCR | ALE ELECTRO-CONSTRUCCIONES SA DE CV | | | SCAC4 |
| 85 | AOCS | AIRLIMO-AIRLINE COURIER SERVICE | | | SCAC3 |
| 86 | AOCS | AO CONTAINER LINES INC | | | SCAC4 |
| 87 | AOCT | ALBERTO, C TRUCKING CO INC | | | SCAC3 |
| 88 | AOCU | INNOSPEC LIMITED | | GB | BIC |
| 89 | AOCU | THE ASSOCIATED OCTEL CO. LTD | | | PWRC |
| 90 | AOCU | Associated Octel | | | RSRV |
| 91 | AOCU | ASSOCIATED OCTEL | | | SCAC3 |
| 92 | AOCU | ASSOCIATED OCTEL CO LTD | | | SCAC4 |
| 93 | AOCV | ADVANCE OCEAN INC. | | | SCAC4 |
| 94 | AOCW | ASTRA OIL COMPANY LLC | | | SCAC4 |
| 95 | AOCX | Aluminum Co. of America | added 4/1953; 7/1954-7/2005 | | NAKINA |
| 96 | AOCX | Aluminum Ore Co. (Alcoa Ore Co.) | 7/1930-7/1932 | | NAKINA |
| 97 | AOCX | Aluminum Ore Co. | 7/1935-1/1952; eliminated 4/1953 | | NAKINA |
| 98 | AOCX | Aluminum Ore Co. | 4/38-1/52 | | NRHS |
| 99 | AOCX | Aluminum Co. of America | 10/57-7/2000 | | NRHS |
| 100 | AOCX | ALUMINUM COMPANY OF AMERICA {ALUMINUM ORE CO.; ALCOA ORE CO.] | | | PWRC |
