| 1 | OT | Aeropelican Air Services Pty Ltd. | ICAO: PEL, Ceased operations on 15 December 2013. Designator PO recalled by IATA | AUS | AVCODES |
| 2 | OT | Avant Airlines, S.A. | ICAO: VAT, Callsign: Avant Airlines, Designator OT* recalled by IATA | RCH | AVCODES |
| 3 | OT | Servicio de Transportes Aereos de Sao Tome | Callsign: Sta, | STP | AVCODES |
| 4 | 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 |
| 5 | OT | Tchadia Airlines | ICAO: CDO, Callsign: Tchadia, Founded in 2018. Commenced operations on 01 October 2018. Ceased operations in August 2022. | TCH | AVCODES |
| 6 | OT | Oregon Trunk Ry. | 1/1975-1/1980 | | NAKINA |
| 7 | OT | Oregon Trunk Ry. | 4/1938-7/1965 | | NAKINA |
| 8 | OT | Oregon Trunk Ry. (Spokane, Portland & Seattle Ry. Co.) | 10/1966 | | NAKINA |
| 9 | OT | Oregon Trunk Ry. (Spokane, Portland & Seattle Ry. Co.) | 7/1923-7/1935 | | NAKINA |
| 10 | OT | Oregon Trunk Ry. | 4/38-7/65 | | NRHS |
| 11 | OT | Oregon Trunk Ry. (Spokane, Portland & Seattle Ry. Co.) | Oct-66 | | NRHS |
| 12 | OT | Oregon Trunk Ry. | 1/75-1/80 | | NRHS |
| 13 | OT | (SPS) OREGON TRUNK RY | | | PWRC |
| 14 | OT | AB Östgötatrafiken | | SE | VKM |
| 15 | OTA | Organizacion de Transportes Aereos, S.A. de C.V. | Callsign: Organizacion, | MEX | AVCODES |
| 16 | OTA | Business Aviators, Inc. | Callsign: Outlaw, | USA | AVCODES |
| 17 | OTA | Organizacion De Transportes Aereos | | | ICAO1 |
| 18 | OTAE | ORTEZ TRANSPORT | | | SCAC4 |
| 19 | OTAG | OSEGUERA TRUCKING CO INC | | | SCAC4 |
| 20 | OTAH | OLSON TRUCKING AND HAULING LLC | | | SCAC4 |
| 21 | OTAI | OT AFRICA LINE LTD | | | SCAC4 |
| 22 | OTAJ | OTA, JAMES, TRUCKING | | | SCAC3 |
| 23 | OTAL | OCEAN TRANSPORT AND LOGISTICS LLC | | | SCAC4 |
| 24 | OTAM | ON-TIME AMERICAN TRANSPORT INC | | | SCAC3 |
| 25 | OTAQ | OTA, KAREN TRUCKING | | | SCAC3 |
| 26 | OTAR | ONE TWO FIVE THREE SIX FIVE EIGHT ( | | | SCAC4 |
| 27 | OTAT | ORCHARDS TRUCK AND AUTO TOWING | | | SCAC3 |
| 28 | OTAT | OPENROAD TRUCKING INC | | | SCAC4 |
| 29 | OTAU | CMA-CGM | | F | BIC |
| 30 | OTAU | OT AFRICA LINE, LTD | | | SCAC3 |
| 31 | OTAU | DELMAS | | | SCAC4 |
| 32 | OTAY | OTAY MESA TRUCKING CORP | | | SCAC3 |
| 33 | OTBO | ORANGE TRUCK BROKERAGE | | | SCAC4 |
| 34 | OTBP | ONE FOUR ONE FOUR ZERO FOUR THREE ( | | | SCAC4 |
| 35 | OTC | Aero-Transportes de Carga, S.A. de C.V. | Callsign: Transporte Carga, | MEX | AVCODES |
| 36 | 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 |
| 37 | OTCE | ONE TWO THREE (123) CAMP TRAILERS | | | SCAC4 |
| 38 | OTCG | ON-TIME CARTAGE INC | | | SCAC3 |
| 39 | OTCH | OTTUMWA COACHES INC | | | SCAC3 |
| 40 | OTCI | ON TIME CARRIERS INC | | | SCAC3 |
| 41 | OTCI | OLMSTED TRANSPORTATION CO INC | | | SCAC4 |
| 42 | OTCK | ORBIT TUNING CORP | | | SCAC4 |
| 43 | OTCL | OCEAN TRAMPING CO LTD | | | SCAC3 |
| 44 | OTCL | ONTRACC LOGISTICS INC | | | SCAC4 |
| 45 | OTCM | OWENS TRUCKING COMPANY | | | SCAC3 |
| 46 | OTCM | OT COMMUNICATIONS | | | SCAC4 |
| 47 | OTCN | OAK TANKER CORPORATION | | | SCAC4 |
| 48 | OTCO | Owensville Terminal Co., Inc. | 7/2000-7/2005 | | NAKINA |
| 49 | OTCO | Owensville Terminal Co., Inc. | Jul-00 | | NRHS |
| 50 | OTCO | OWENSVILLE TERMINAL COMPANY | | | PWRC |
| 51 | OTCO | Owensville Terminal | | | RSRV |
| 52 | OTCO | OWENSVILLE TERMINAL CO INC | | | SCAC4 |
| 53 | OTCP | OWENS, T C TRUCKING CO INC | | | SCAC3 |
| 54 | OTCQ | OSBORNE TRUCKING COMPANY | | | SCAC3 |
| 55 | OTCR | Oakdale Traction Corp. | 7/2005 | | NAKINA |
| 56 | OTCR | OAKDALE TRACTION CORPORATION | | | PWRC |
| 57 | OTCR | Oakdale Traction Corporation | | | RSRV |
| 58 | OTCR | OAKDALE TRACTION CORPORATION | | | SCAC4 |
| 59 | OTCT | OTC TRANSPORT CORPORATION | | | SCAC3 |
| 60 | OTCT | Oil Terminal Constanta | | RO | TRAFFIC |
| 61 | OTCV | OTC TRANSPORTATION SERVICES INC | | | SCAC4 |
| 62 | OTCY | OLYMPIC TRANSPORT COMPANY INC | | | SCAC3 |
| 63 | OTDA | ON THE DOUBLE AIR EXPRESS INC | | | SCAC3 |
| 64 | OTDI | O T D INC | | | SCAC3 |
| 65 | OTDN | ON-TIME DELIVERY INC | | | SCAC4 |
| 66 | OTDQ | ON TIME DELIVERY | | | SCAC4 |
| 67 | OTDR | OUTDOOR TRADITION TOURS INC | | | SCAC3 |
| 68 | OTDS | ON TIME DELIVERY INC | | | SCAC4 |
| 69 | OTDV | O T DELIVERY SYSTEMS INC | | | SCAC3 |
| 70 | OTDV | O T DELIVERY SYSTEMS INC | | | SCAC4 |
| 71 | OTDW | ON THE DOUBLE WORLDWIDE COURIER LTD | | | SCAC3 |
| 72 | OTDW | OTD LOGISTICS INCORPORATED | | | SCAC4 |
| 73 | OTDX | Greenbrier Management Services, LLC | added 7/2005; 7/2005 | | NAKINA |
| 74 | OTDX | Greenbrier Leasing Corp. | added 1/1980; 1/1980-7/2000; eliminated 7/2005 | | NAKINA |
| 75 | OTDX | O-T-D Corp. | added 4/1958; 4/1961-1/1975; eliminated 1/1980 | | NAKINA |
| 76 | OTDX | O-T-D Corp. | 4/61-1/75; eliminated 1/80 | | NRHS |
| 77 | OTDX | Greenbrier Leasing Corp. | added 1/80; 1/80-7/2000 | | NRHS |
| 78 | OTDX | *O-T-D CORP. | | | PWRC |
| 79 | OTDX | +GREENBRIER MANAGEMENT SERVICES [GREENBRIER LEASING CORPORATION]) | | | PWRC |
| 80 | OTDX | Greenbrier Leasing Corporation | | | RSRV |
| 81 | OTDX | O-T-D CORP | | | SCAC3 |
| 82 | OTDX | GREENBRIER MANAGEMENT SERVICES LLC | | | SCAC4 |
| 83 | OTDY | ON TIME DELIVERY INC | | | SCAC3 |
| 84 | OTE | BAe Military Division Warton | Callsign: Octane, | GB | AVCODES |
| 85 | OTEB | ONE TWO SIX SEVEN EIGHT SEVEN THREE | | | SCAC4 |
| 86 | OTEE | ONE THREE EIGHT SIX NINE N | | | SCAC4 |
| 87 | OTEG | ON-TIME EXPRESS & LOGISTICS INC | | | SCAC4 |
| 88 | OTEI | OTTER EXPRESS INC | | | SCAC3 |
| 89 | OTEN | OSBURN TRUCKING ENTERPRISES INCORPO | | | SCAC3 |
| 90 | OTEN | ONE TWO EIGHT EIGHT NINE FOUR FOUR | | | SCAC4 |
| 91 | OTEQ | ON TIME EXPRESS INC | | | SCAC4 |
| 92 | OTER | ON TRACK EXPRESS | | | SCAC4 |
| 93 | OTES | ONTIME EXPEDITED SERVICES INC | | | SCAC3 |
| 94 | OTEU | CAI INTERNATIONAL | | USA | BIC |
| 95 | OTEU | CONSENT EQUIPMENT AB SWEDEN | | | SCAC3 |
| 96 | OTEU | CONSENT EQUIPMENT AB | | | SCAC4 |
| 97 | OTEV | OP-TECH ENVIRONMENTAL SERVICES INC | | | SCAC4 |
| 98 | OTEW | ON TIME EXPRESS INC | | | SCAC4 |
| 99 | OTEX | Otex Tank Car Co. | 1/1943-1/1946 | | NAKINA |
| 100 | OTEX | OTEX TANK CAR CO. | | | PWRC |
