| 1 | OB | Astrakhan Airlines | ICAO: ASZ, Callsign: Air Astrakhan, IATA Prefix: 562, Designator OB recalled by IATA | RUS | AVCODES |
| 2 | OB | Shepparton Airlines | Designator recalled by IATA | AUS | AVCODES |
| 3 | OB | Oasis International Airlines | ICAO: AAN, Callsign: Oasis, Ceased operations in December 1996 | E | AVCODES |
| 4 | OB | Austrian Airtransport (Osterreichische Flugbetriebsgesellschaft MbH.) | ICAO: AAT, Callsign: Austrian Charter, ICAO designator changed from AUC | A | AVCODES |
| 5 | OB | Austrian Airtransport (Osterreiechische Flugbetriebsgesellschaft mbH.) | ICAO: AUC, Callsign: Aircharter, ICAO callsign changed to Austrain Aircharter. Charter subsidary of Austrian Airlines | A | AVCODES |
| 6 | OB | Austrian Airtransport (Osterreiechische Flugbetriebsgesellschaft mbH.) | ICAO: AUC, Callsign: Austrian charter, ICAO callsign changed from Aircharter. Charter subsidary of Austrian Airlines | A | AVCODES |
| 7 | OB | Air Bee S.p.A. | ICAO: CMM, | I | AVCODES |
| 8 | OB | Boliviana de Aviacion (BoA) | ICAO: BOV, Callsign: Boliviana, IATA Prefix: 930, Founded on 24 October 2007 | BOL | AVCODES |
| 9 | OBA | Aerobanana, S.A. de C.V. | Callsign: Aerobanana, | MEX | AVCODES |
| 10 | OBA | Aerobanana | | | ICAO1 |
| 11 | OBA | Ofotbanen | | N | TRAFFIC |
| 12 | OBAG | OASIS BAGS | | | SCAC4 |
| 13 | OBAQ | OBA PRODUCE COMPANY | | | SCAC3 |
| 14 | OBAQ | OBC NEDERLAND LIMITED | | | SCAC4 |
| 15 | OBAR | OBARA & BREHM TRANSFER INC | | | SCAC4 |
| 16 | OBAS | OBRIEN & SMITH TRUCKING CO | | | SCAC3 |
| 17 | OBAS | Ofotbanen | | NO | VKM |
| 18 | OBB | Österreichische Budesbahn | | A | TRAFFIC |
| 19 | OBB | Österreichische Bundesbahnen | | AT | VKM |
| 20 | OBBL | Orange & Black Bus Lines | | USA | TRAFFIC |
| 21 | OBBP | ÖBB Postbus | | A | TRAFFIC |
| 22 | OBBPB | Österreichische Postbus AG | | A | TRAFFIC |
| 23 | OBBT | OTOS, BILL BOAT TRAILERING (HAULING | | | SCAC3 |
| 24 | OBC | Olympic Broadcasting Services | | GB | AVCODES |
| 25 | OBCC | OLENICK BROS COAL CO | | | SCAC3 |
| 26 | OBCC | O B C NORTHWEST INC | | | SCAC4 |
| 27 | OBCG | O'BRIEN CARTAGE CO | | | SCAC3 |
| 28 | OBCG | OBRIEN CARTAGE CO | | | SCAC4 |
| 29 | OBCI | OCEAN BULK CARRIERS INC, | | | SCAC3 |
| 30 | OBCI | OCEANIC BULK CARRIERS LTD | | | SCAC4 |
| 31 | OBCU | N.V. COBO CONSTRUCTION | | SME | BIC |
| 32 | OBCU | ORBICON | | | SCAC3 |
| 33 | OBCU | ORBICON | | | SCAC4 |
| 34 | OBCX | The Neatsfoot Oil Refineries Corp. | 7/1935-4/1938 | | NAKINA |
| 35 | OBCX | The Neatsfoot Oil Refineries Corp. | Apr-38 | | NRHS |
| 36 | OBCX | NEATSFOOT OIL REFINERIES CORP. | | | PWRC |
| 37 | OBDC | ORANGE & BLUE DISTRIBUTING COMPANY | | | SCAC3 |
| 38 | OBDE | OBION DENTON COMPANY | | | SCAC3 |
| 39 | OBDS | ORME, BILL DELIVERY SERICES INC | | | SCAC4 |
| 40 | OBDU | OLD BUSHMILLS DISTILLERY, LTD | | | SCAC3 |
| 41 | OBE | Air Bee S.p.A. | IATA: BM, Suspended operations 10 September 2008. | I | AVCODES |
| 42 | OBEA | OBES, ANDREW SON | | | SCAC3 |
| 43 | OBED | OBER, DOUG | | | SCAC3 |
| 44 | OBEL | OBELE TRUCKING | | | SCAC3 |
| 45 | OBEL | ONTARIO BELTING LTD | | | SCAC4 |
| 46 | OBEM | OBERMEIR, GEORGE RUDOLPH | | | SCAC3 |
| 47 | OBEN | OBRIEN TRUCKING CO INC | | | SCAC3 |
| 48 | OBEP | OCEAN BLUE EXPRESS INC | | | SCAC4 |
| 49 | OBET | OBERT TRUCKING COMPANY | | | SCAC3 |
| 50 | OBEV | Osning-Bahn e.V. | | DE | VKM |
| 51 | OBFR | OBRIEN FREIGHT SYSTEMS INC | | | SCAC3 |
| 52 | OBFR | ORANGE BLOSSOM FARM | | | SCAC4 |
| 53 | OBGP | OUTBOUND GROUP, THE | | | SCAC4 |
| 54 | OBHG | OPERATION BLESSING OB HUNGER STRIKE | | | SCAC4 |
| 55 | OBI | Amedair Nig. Ltd. | Callsign: Amedair, | WAN | AVCODES |
| 56 | OBIG | OCEANIC BRIDGE INTERNATIONAL INC | | | SCAC4 |
| 57 | OBII | ORIGINAL BEER IMPORTING & DISTRUBUT | | | SCAC3 |
| 58 | OBIS | ORBIS LOGISTICS | | | SCAC4 |
| 59 | OBJ | Comunicacion Global Objetivo, S.L. | Callsign: Objetivo, | E | AVCODES |
| 60 | OBJ | Ohs Bruks Järnvägs museiförening | | SE | VKM |
| 61 | OBK | Amako Airlines Limited. | Callsign: Amako Air, | WAN | AVCODES |
| 62 | OBK | Amako Airlines | | | ICAO1 |
| 63 | OBKG | ORION BULKERS GMBH & CO KG | | | SCAC4 |
| 64 | OBKS | OCEAN BULK SHIPS, INC. | | | SCAC3 |
| 65 | OBL | ONEONTA BUS LINES INC | | | SCAC4 |
| 66 | OBLA | O-B LEASING | | | SCAC3 |
| 67 | OBLK | OHIO BULK TRANSFER CO | | | SCAC4 |
| 68 | OBLS | OUTER BANKS LIMOUSINE SERVICE INC | | | SCAC3 |
| 69 | OBLU | PT OCEAN BUANA LOGISTICS | | | SCAC4 |
| 70 | OBM | Aviaobshemash | Callsign: Obshemash, | RUS | AVCODES |
| 71 | OBMC | OYSTER BAY MOVING CORP | | | SCAC3 |
| 72 | OBMC | O B MACARONI CO | | | SCAC4 |
| 73 | OBMG | OSBORN MOVING | | | SCAC3 |
| 74 | OBMG | OAK BAY MARINE GROUP | | | SCAC4 |
| 75 | OBMJ | OBRIEN, MAURICE J | | | SCAC3 |
| 76 | OBMK | OBRIEN, MIKE SPECIALIZED HAULING IN | | | SCAC4 |
| 77 | OBMP | OBRIEN MOTORSPORTS | | | SCAC4 |
| 78 | OBMQ | OBRIEN MOVING AND STORAGE CO | | | SCAC3 |
| 79 | OBMR | OBERMEYER TRANSFER CO | | | SCAC3 |
| 80 | OBMS | OBRIENS MOVING & STORAGE, INC | | | SCAC3 |
| 81 | OBMV | OBRIEN MOVERS INC | | | SCAC3 |
| 82 | OBMZ | OLD BEN #21 MINE | | | PWRC |
| 83 | OBNM | OBRIENS MOVING & STORAGE | | | SCAC4 |
| 84 | OBNQ | OBORN TRANSFER AND STORAGE COMPANY | | | SCAC3 |
| 85 | OBNQ | OBORN TRANSFER AND STORAGE COMPANY | | | SCAC4 |
| 86 | OBNT | OBRIEN TRANSPORT CORPORATION | | | SCAC3 |
| 87 | OBNT | OBREGON AUTOTRANSPORTES | | | SCAC4 |
| 88 | OBNV | OBELISK NAVIGATION S A | | | SCAC3 |
| 89 | OBNV | OBELISK E N E | | | SCAC4 |
| 90 | OBPA | *RETIRED 04-15-93 ATP (580) | | | PWRC |
| 91 | OBPA | *OGDENSBURG BRIDGE & PORT AUTHORITY | | | PWRC |
| 92 | OBPA | OGDENSBURG BRIDGE & PORT AUTHORITY | | | SCAC3 |
| 93 | OBPI | OB PRODUCE INC | | | SCAC4 |
| 94 | OBPN | OSBORNE PANAMA, S.A. | | | SCAC3 |
| 95 | OBRC | OBRIEN COMPANY | | | SCAC3 |
| 96 | OBRE | OBREGON RAMIREZ, OTILIA | | | SCAC4 |
| 97 | OBRF | OBRIEN, FRANK | | | SCAC3 |
| 98 | OBRG | OBERG FREIGHT COMPANY | | | SCAC4 |
| 99 | OBRJ | OBRIEN, JOHN E | | | SCAC3 |
| 100 | OBRN | O'BRIEN&NYE CARTAGE CO | | | SCAC3 |
