| 1 | OO | SkyWest Airlines | ICAO: SKW, Callsign: Skywest, IATA Prefix: 302, Name changed from Sky West Airlines | USA | AVCODES |
| 2 | OO | Sky West Airlines | ICAO: SKW, Callsign: Skywest, IATA Prefix: 302, Name changed to SkyWest Airlines | USA | AVCODES |
| 3 | OOAK | ONE OF A KIND TOURS INC | | | SCAC3 |
| 4 | OOAK | OOSTLANDER, JEANNETTE | | | SCAC4 |
| 5 | OOCC | OOCL (CANADA) INC | | | SCAC3 |
| 6 | OOCC | OOCL (CANADA) INC | | | SCAC4 |
| 7 | OOCL | ORIENT OVERSEAS CONTAINER LINE, INC. | | | PWRC |
| 8 | OOCL | ORIENT OVERSEAS CONTAINER LINE, INC | | | SCAC3 |
| 9 | OOCO | OLIVER OIL CO INC | | | SCAC3 |
| 10 | OOCO | OOCL LOGISTICS LINE LIMITED | | | SCAC4 |
| 11 | OOCU | ORIENT OVERSEAS CONTAINER LINE LTD. | | HK | BIC |
| 12 | OOCZ | ORIENT OVERSEAS CONTAINER LINE, INC. | | | PWRC |
| 13 | OOCZ | Orient Overseas Line | | | RSRV |
| 14 | OOCZ | ORIENT OVERSEAS LINE, INC. | | | SCAC4 |
| 15 | OOE | Air Operations of Europe | Callsign: Air Ops, Ceased operations in 1996. | S | AVCODES |
| 16 | OOEI | OHIO ONTARIO EXPRESS INC | | | SCAC3 |
| 17 | OOEI | OHIO ONTARIO EXPRESS INC | | | SCAC4 |
| 18 | OOFA | ONE ONE FOUR TWO NINE EIGHT FIVE (1 | | | SCAC4 |
| 19 | OOFD | ONE ONE FOUR THREE SEVEN SIX | | | SCAC4 |
| 20 | OOFS | ONE ONE FIVE SIX SEVEN TWO NINE (11 | | | SCAC4 |
| 21 | OOGC | ORMOND OIL AND GAS COMPANY INC | | | SCAC4 |
| 22 | OOIC | OWNERS & OPERATORS INC | | | SCAC4 |
| 23 | OOIL | ORANGE OIL CO INC | | | SCAC4 |
| 24 | OOKG | OMARO TRUCKING | | | SCAC4 |
| 25 | OOLC | ORIENT OVERSEAS CONTAINER LINE, INC. | | | PWRC |
| 26 | OOLC | ORIENT OVERSEAS CONTAINER LINE, INC | | | SCAC3 |
| 27 | OOLG | OPTION ONE LOGISTICS | | | SCAC4 |
| 28 | OOLL | ORIENT OVERSEAS CONTAINER LINE LIMI | | | SCAC4 |
| 29 | OOLU | ORIENT OVERSEAS CONTAINER LINE LTD. | | HK | BIC |
| 30 | OOLU | ORIENT OVERSEAS CONTAINER LINE, INC. | | | PWRC |
| 31 | OOLU | Orient Overseas Container Line | | | RSRV |
| 32 | OOLU | ORIENT OVERSEAS CONTAINER LINE INC | | | SCAC3 |
| 33 | OOLU | ORIENT OVERSEAS CONTAINER LINE LTD | | | SCAC4 |
| 34 | OOLY | OKUNFULURE, OLUBIYISOLA | | | SCAC4 |
| 35 | OOM | Zoom Airlines, Inc. | IATA: Z4, Callsign: Zoom, IATA Prefix: 389, Ceased Operations and filed for Bankruptcy protection on 28 August 2008. | CDN | AVCODES |
| 36 | OOM | Zoom Airlines | IATA: Z4 | | ICAO1 |
| 37 | OOND | ONE TWO SEVEN ONE SIX SIX | | | SCAC4 |
| 38 | OONE | ONE ONE NINE EIGHT TWO THREE FOUR ( | | | SCAC4 |
| 39 | OOOC | ONE ON ONE CARRIERS INC | | | SCAC3 |
| 40 | OOOC | ONE ON ONE CARRIERS INC | | | SCAC4 |
| 41 | OOOX | Osborne, Inc. | added 10/1997; eliminated 4/1998; 7/2000-7/2005 (not listed) | | NAKINA |
| 42 | OOOX | Osborne, Inc. | added 10/97; eliminated 4/98; 7/2000 | | NRHS |
| 43 | OOOX | OSBORNE INCORPORATED | | | PWRC |
| 44 | OOOX | Osborne | | | RSRV |
| 45 | OOPC | OWNER OPERATORS PETROLEUM CORP | | | SCAC3 |
| 46 | OORX | Chartrand's Traffic Service | eliminated 10/1959 | | NAKINA |
| 47 | OORX | Chartrand's Tank Car Service, Inc. | added 10/1958 | | NAKINA |
| 48 | OORX | Chartrand's Tank Car Service | added 4/1958; eliminated 10/1958 | | NAKINA |
| 49 | OORX | Chartrand's Tank Car Rentals | added 1/1958; eliminated 4/1958 | | NAKINA |
| 50 | OORX | Chartrand's Tank Car Service | added 7/1953; 7/1954-10/1957; eliminated 1/1958 | | NAKINA |
| 51 | OORX | Chartrand's Traffic Service | 1/1952; eliminated 7/1953 | | NAKINA |
| 52 | OORX | Opelousas Oil Refinery | 4/1947 (not listed); 1/1950 | | NAKINA |
| 53 | OORX | Chartrand's Traffic Service | Jan-52 | | NRHS |
| 54 | OORX | Chartrand's Tank Car Service | 10/57; eliminated 1/58 | | NRHS |
| 55 | OORX | Chartrand's Tank Car Rentals | added 1/58; eliminated 10/58 | | NRHS |
| 56 | OORX | Chartrand's Tank Car Service, Inc. | added 10/58 | | NRHS |
| 57 | OORX | Chartrand's Traffic Service | eliminated 10/59 | | NRHS |
| 58 | OORX | CHARTRAND'S TANK CAR SERVICE (OPELOUSAS OIL REFINERY) | | | PWRC |
| 59 | OOS | Ostravské opravny a strojírny, s.r.o. | | CZ | VKM |
| 60 | OOSA | OOST ATLANTIC LIJN BV | | | SCAC4 |
| 61 | OOSL | ONE ONE SIX FIVE THREE FOUR FIVE (1 | | | SCAC4 |
| 62 | OOST | OOSTDYK, ENGLE, INC | | | SCAC3 |
| 63 | OOST | OOSTDYK, ENGLE, INC | | | SCAC4 |
| 64 | OOST | Oostnet | | NL | TRAFFIC |
| 65 | OOT | Out of the Blue Air Safaris (PTY) Ltd. | Callsign: Ootbas, | ZA | AVCODES |
| 66 | OOT | Out Of The Blue Air Safaris | | | ICAO1 |
| 67 | OOTA | ONE ONE THREE ZERO ZERO | | | SCAC4 |
| 68 | OOTG | OPTION ONE TRANSPORTATION GROUP LLC | | | SCAC4 |
| 69 | OOTP | OPT OVERSEAS TRANSPORT | | | SCAC4 |
| 70 | OOTU | OTLO SHIPPING LINE | | UAE | BIC |
| 71 | OOTW | ONE ONE TWO (112) WELLINGTON STREET | | | SCAC4 |
| 72 | OOUI | OWNER OPERATOR UNION INC | | | SCAC4 |
| 73 | OOUU | ORIENT OVERSEAS LINE, INC. | | | PWRC |
| 74 | OOUU | Orient Overseas Line | | | RSRV |
| 75 | OOUU | ORIENT OVERSEAS CONTAINER LTD | | | SCAC3 |
| 76 | OOUU | OCEANEERING INTERNATIONAL LIMITED | | | SCAC4 |
| 77 | OOVL | ONE THOUSAND OAKS VAN LINES (1000 O | | | SCAC3 |
| 78 | OOWH | OUR OWN HARDWARE CO | | | SCAC3 |
| 79 | OOXL | ONTARIO-OHIO EXPRESS LTD | | | SCAC3 |
| 80 | OOZN | ONE ONE ZERO NINE ONE SEVEN THREE ( | | | SCAC4 |
