| 3501 | OSTO | ONE SEVEN THREE ONE NINE THREE (173 | | | SCAC4 |
| 3502 | OSTP | OSBORN TRANSPORTATION INC | | | SCAC3 |
| 3503 | OSTP | OSBORN TRANSPORTATION INC | | | SCAC4 |
| 3504 | OSTQ | OSBORN TRANSFER INC | | | SCAC3 |
| 3505 | OSTR | O & S TRANSPORTATION INC | | | SCAC3 |
| 3506 | OSTR | Miejski Zakład Komunikacji w Ostrołęce | | PL | TRAFFIC |
| 3507 | OSTRA | Osterwalder Transport AG | | CH | VKM |
| 3508 | OSTS | OVERSEAS TEXAS CITY LLC | | | SCAC4 |
| 3509 | OSTT | OST TRUCKING, INC | | | SCAC3 |
| 3510 | OSTT | OILFIELD SERVICE & TRUCKING/OST TRU | | | SCAC4 |
| 3511 | OSTU | SUNCONTRACT GMBH | | CH | BIC |
| 3512 | OSTU | OSTAB | | | SCAC3 |
| 3513 | OSTV | OUTHOUSE, STEVE TRUCKING INC | | | SCAC3 |
| 3514 | OSTV | OSTROV DOORS LTD | | | SCAC4 |
| 3515 | OSTW | OCEAN STAR TRANSPORTATION LLC | | | SCAC4 |
| 3516 | OSTX | New York Oil Storage & Transfer Co. | 8/1920 | | NAKINA |
| 3517 | OSTX | NEW YORK OIL STORAGE & TRANSFER CO. | | | PWRC |
| 3518 | OSU | Ohio State University Flight Education Division | Callsign: Scarlet, | USA | AVCODES |
| 3519 | OSUI | OSUMI TRUCKING | | | SCAC3 |
| 3520 | OSV | Vladikavkaz State Air Enterprise | Callsign: Irair, | RUS | AVCODES |
| 3521 | OSVA | OFFSHORE SERVICE VESSELS LLC | | | SCAC4 |
| 3522 | OSVC | OLSON SERVICE CO | | | SCAC4 |
| 3523 | OSVE | ONE SEVEN THREE THREE (1733) EXPRES | | | SCAC4 |
| 3524 | OSVL | OCEAN SERVICES LLC | | | SCAC4 |
| 3525 | OSVT | ONE SEVEN TWO SEVEN EIGHT THREE (17 | | | SCAC3 |
| 3526 | OSVT | ONE THREE SEVEN SEVEN SIX ZERO SIX | | | SCAC4 |
| 3527 | OSW | Jetafrica Swaziland | Callsign: Bevo, | SD | AVCODES |
| 3528 | OSW | JetAfrica Swaziland | | | ICAO1 |
| 3529 | OSWA | OSTRIA WAVES LTD - MARSHALL ISLANDS | | | SCAC4 |
| 3530 | OSWI | MZK Oswiecim | | PL | TRAFFIC |
| 3531 | OSWO | OSWEGO OIL SERVICE | | | SCAC3 |
| 3532 | OSWR | OLD STANDARD WOOD | | | SCAC4 |
| 3533 | OSWT | ONE STOP TOWING & TRANSPORT | | | SCAC4 |
| 3534 | OSXI | OLD STAR TRANSPORT INC | | | SCAC4 |
| 3535 | OSXN | ONE SOURCE TRANSPORTATION | | | SCAC4 |
| 3536 | OSXP | OHIO SOUTHERN EXPRES INC | | | SCAC3 |
| 3537 | OSXP | OFFSHORE EXPRESS INC | | | SCAC4 |
| 3538 | OSY | Open Skies Consultative Commission (OSCC) | Callsign: Open Skies, | USA | AVCODES |
| 3539 | OSY | Open Skies Consultative Commission | IATA: 1L | | ICAO1 |
| 3540 | OSY | Odikes Sygkinonies | City: Athen | GR | TRAFFIC |
| 3541 | OSYC | ONE (1) SLY TRANSPORT CORP | | | SCAC4 |
| 3542 | OSYI | OMEGA SYSTEMS INC | | | SCAC3 |
| 3543 | OSYK | OSYKA TRUCKING INC | | | SCAC3 |
| 3544 | OSYT | OUTSOURCING SERVICES AND TRADING SO | | | SCAC4 |
| 3545 | OSZ | OTTAWA SILICA | | | PWRC |
| 3546 | OSZC | ONE SEVEN ONE FIVE SEVEN ZERO (1715 | | | SCAC4 |
| 3547 | OSZN | ONE SIX ZERO NINE NINE NINE ZERO (1 | | | SCAC4 |
| 3548 | OSZT | ONE SIX ZERO THREE EIGHT EIGHT (160 | | | SCAC4 |
| 3549 | OT | Aeropelican Air Services Pty Ltd. | ICAO: PEL, Ceased operations on 15 December 2013. Designator PO recalled by IATA | AUS | AVCODES |
| 3550 | OT | Avant Airlines, S.A. | ICAO: VAT, Callsign: Avant Airlines, Designator OT* recalled by IATA | RCH | AVCODES |
| 3551 | OT | Servicio de Transportes Aereos de Sao Tome | Callsign: Sta, | STP | AVCODES |
| 3552 | OT | Lastp-Linhas Aereas de Sao Tome E Principe (Sao Tome And Principe Airlines) | ICAO: OTN, Callsign: Sta, ICAO desigantor changed to STP | STP | AVCODES |
| 3553 | OT | Tchadia Airlines | ICAO: CDO, Callsign: Tchadia, Founded in 2018. Commenced operations on 01 October 2018. Ceased operations in August 2022. | TCH | AVCODES |
| 3554 | OT | Oregon Trunk Ry. | 1/1975-1/1980 | | NAKINA |
| 3555 | OT | Oregon Trunk Ry. | 4/1938-7/1965 | | NAKINA |
| 3556 | OT | Oregon Trunk Ry. (Spokane, Portland & Seattle Ry. Co.) | 10/1966 | | NAKINA |
| 3557 | OT | Oregon Trunk Ry. (Spokane, Portland & Seattle Ry. Co.) | 7/1923-7/1935 | | NAKINA |
| 3558 | OT | Oregon Trunk Ry. | 4/38-7/65 | | NRHS |
| 3559 | OT | Oregon Trunk Ry. (Spokane, Portland & Seattle Ry. Co.) | Oct-66 | | NRHS |
| 3560 | OT | Oregon Trunk Ry. | 1/75-1/80 | | NRHS |
| 3561 | OT | (SPS) OREGON TRUNK RY | | | PWRC |
| 3562 | OT | AB Östgötatrafiken | | SE | VKM |
| 3563 | OTA | Organizacion de Transportes Aereos, S.A. de C.V. | Callsign: Organizacion, | MEX | AVCODES |
| 3564 | OTA | Business Aviators, Inc. | Callsign: Outlaw, | USA | AVCODES |
| 3565 | OTA | Organizacion De Transportes Aereos | | | ICAO1 |
| 3566 | OTAE | ORTEZ TRANSPORT | | | SCAC4 |
| 3567 | OTAG | OSEGUERA TRUCKING CO INC | | | SCAC4 |
| 3568 | OTAH | OLSON TRUCKING AND HAULING LLC | | | SCAC4 |
| 3569 | OTAI | OT AFRICA LINE LTD | | | SCAC4 |
| 3570 | OTAJ | OTA, JAMES, TRUCKING | | | SCAC3 |
| 3571 | OTAL | OCEAN TRANSPORT AND LOGISTICS LLC | | | SCAC4 |
| 3572 | OTAM | ON-TIME AMERICAN TRANSPORT INC | | | SCAC3 |
| 3573 | OTAQ | OTA, KAREN TRUCKING | | | SCAC3 |
| 3574 | OTAR | ONE TWO FIVE THREE SIX FIVE EIGHT ( | | | SCAC4 |
| 3575 | OTAT | ORCHARDS TRUCK AND AUTO TOWING | | | SCAC3 |
| 3576 | OTAT | OPENROAD TRUCKING INC | | | SCAC4 |
| 3577 | OTAU | CMA-CGM | | F | BIC |
| 3578 | OTAU | OT AFRICA LINE, LTD | | | SCAC3 |
| 3579 | OTAU | DELMAS | | | SCAC4 |
| 3580 | OTAY | OTAY MESA TRUCKING CORP | | | SCAC3 |
| 3581 | OTBO | ORANGE TRUCK BROKERAGE | | | SCAC4 |
| 3582 | OTBP | ONE FOUR ONE FOUR ZERO FOUR THREE ( | | | SCAC4 |
| 3583 | OTC | Aero-Transportes de Carga, S.A. de C.V. | Callsign: Transporte Carga, | MEX | AVCODES |
| 3584 | OTC | Air Travel Co., Ltd. | IATA: A6, Callsign: Air Travel, IATA Prefix: 389, Name changed from Yunnan Hong Tu Airlines Co., Ltd. ICAO designator changed from HTU. | PRC | AVCODES |
| 3585 | OTCE | ONE TWO THREE (123) CAMP TRAILERS | | | SCAC4 |
| 3586 | OTCG | ON-TIME CARTAGE INC | | | SCAC3 |
| 3587 | OTCH | OTTUMWA COACHES INC | | | SCAC3 |
| 3588 | OTCI | ON TIME CARRIERS INC | | | SCAC3 |
| 3589 | OTCI | OLMSTED TRANSPORTATION CO INC | | | SCAC4 |
| 3590 | OTCK | ORBIT TUNING CORP | | | SCAC4 |
| 3591 | OTCL | OCEAN TRAMPING CO LTD | | | SCAC3 |
| 3592 | OTCL | ONTRACC LOGISTICS INC | | | SCAC4 |
| 3593 | OTCM | OWENS TRUCKING COMPANY | | | SCAC3 |
| 3594 | OTCM | OT COMMUNICATIONS | | | SCAC4 |
| 3595 | OTCN | OAK TANKER CORPORATION | | | SCAC4 |
| 3596 | OTCO | Owensville Terminal Co., Inc. | 7/2000-7/2005 | | NAKINA |
| 3597 | OTCO | Owensville Terminal Co., Inc. | Jul-00 | | NRHS |
| 3598 | OTCO | OWENSVILLE TERMINAL COMPANY | | | PWRC |
| 3599 | OTCO | Owensville Terminal | | | RSRV |
| 3600 | OTCO | OWENSVILLE TERMINAL CO INC | | | SCAC4 |
