| 1 | OM | Monarch Airlines Ltd. | ICAO: MON, Callsign: Monarch, IATA designator changed to ZB | GB | AVCODES |
| 2 | OMA | Oman Air | Callsign: Khanjar, ICAO callsign changed from Oman Air | OM | AVCODES |
| 3 | OMA | Oman Air | Callsign: Oman Air, ICAO callsign changed to Khanjar | OM | AVCODES |
| 4 | OMA | Oman Air | IATA: WY, Callsign: Oman Air, IATA Prefix: 910, ICAO callsign changed from Khanjar | OM | AVCODES |
| 5 | OMA | Ontario Metro Airlines Ltd. | Callsign: Ontario Metro, | CDN | AVCODES |
| 6 | OMA | Oman Air | IATA: WY | | ICAO1 |
| 7 | OMA | Oman Air | | OM | TRAFFIC |
| 8 | OMAB | OLIVARES, MARIO ALBERTO | | | SCAC4 |
| 9 | OMAE | OMA ENTERTAINMENT, INC | | | SCAC4 |
| 10 | OMAK | ONCUE MARKETING LLC | | | SCAC4 |
| 11 | OMAO | OMEGA MARITIME INC | | | SCAC4 |
| 12 | OMAR | OMARA MOVING & STORAGE INC | | | SCAC3 |
| 13 | OMAR | OMARA MOVING & STORAGE INC | | | SCAC4 |
| 14 | OMAS | OASIS MOVING & STORAGE | | | SCAC4 |
| 15 | OMAT | OMA TRUCKING INC | | | SCAC4 |
| 16 | OMAT | Metro Area Transit | City: Omaha (NE) | USA | TRAFFIC |
| 17 | OMAU | OMNI TANKER PTY LTD | | AUS | BIC |
| 18 | OMAU | OCEAN MARINE LINE | | | SCAC3 |
| 19 | OMAX | Omaha Public Power District | added 1/1978; 1/1980-7/2005 | | NAKINA |
| 20 | OMAX | Omaha Public Power District | added 1/78; 1/80-7/2000 | | NRHS |
| 21 | OMAX | OMAHA PUBLIC POWER DISTRICT | | | PWRC |
| 22 | OMAX | Omaha Public Power District | | | RSRV |
| 23 | OMAX | OMAHA PUBLIC POWER DISTRICT | | | SCAC4 |
| 24 | OMAY | ORTH-MAYFLOWER | | | SCAC3 |
| 25 | OMB | Omni-blu Aviation Limited | IATA: O7, Callsign: Omniblu, | WAN | AVCODES |
| 26 | OMB | Odense - Middelfart Banen (Nordvestfyenske Jernbane) | 1911 - 1966 | DK | jernbanen.dk |
| 27 | OMB | Odense - Middelfart Banen (Nordvestfyenske Jernbane) | 1911 - 1966 | DK | TRAFFIC |
| 28 | OMBC | ORIGINAL MAPLE BAT CORPORATION, THE | | | SCAC4 |
| 29 | OMBS | OMNIBLUE SHIPPING INC | | | SCAC4 |
| 30 | OMBT | OMNIBUS TOURS | | | SCAC3 |
| 31 | OMBU | MISSIONLINE LOGISTICS SA | | RA | BIC |
| 32 | OMBU | Omnibox Container Management Services | | | RSRV |
| 33 | OMBU | OMNIBOX CONTAINER MANAGEMENT SERVIC | | | SCAC4 |
| 34 | OMCA | OMCAN MANUFACTURING & DISTRIBUTING | | | SCAC4 |
| 35 | OMCC | OMC CARRIERS LLC | | | SCAC4 |
| 36 | OMCI | OWENS MOTOR COACH INC | | | SCAC3 |
| 37 | OMCL | ONWARD MANUFACTURING COMPANY LIMITE | | | SCAC4 |
| 38 | OMCN | O & M CONSTRUCTION CO | | | SCAC3 |
| 39 | OMCN | OHIO MATTRESS CO LICENSING AND COMP | | | SCAC4 |
| 40 | OMCO | OCEANSTAR MARITIME CO | | | SCAC4 |
| 41 | OMCP | ORION MARINE CORPORATION | | | SCAC3 |
| 42 | OMCP | ORION MARINE CORPORATION | | | SCAC4 |
| 43 | OMCQ | OMNISHIP MARITIME COMPANY LIMITED | | | SCAC3 |
| 44 | OMCS | ORANGE-MARTIN CONVALESCENT SERVICE | | | SCAC3 |
| 45 | OMCT | OMC TRUCKING | | | SCAC3 |
| 46 | OMCT | OMC AUTO TRANSPORT LLC | | | SCAC4 |
| 47 | OMCU | CHEMPROD NOMINEES PTY LTD | | | SCAC4 |
| 48 | OMCX | O-M Corp. | 1/1975-1/1980 | | NAKINA |
| 49 | OMCX | O-M Corp. | 1/75-1/80 | | NRHS |
| 50 | OMCX | O-M CORP. | | | PWRC |
| 51 | OMCY | ORAMA MARITIME COMPANY | | | SCAC4 |
| 52 | OMCZ | OKEENE MILLING COMPANY | | | PWRC |
| 53 | OMD | Nomadic Aviation Group LLC t/a Nomadic Aviation | Callsign: Nomadic, | USA | AVCODES |
| 54 | OMDI | OMEDI RAMIREZ, GLADYS | | | SCAC4 |
| 55 | OMDS | OMEGA DISTRIBUTION SERVICES INC | | | SCAC3 |
| 56 | OME | Omega Air, S. de R.L. | | HN | AVCODES |
| 57 | OME | Omega Aerial Refueling Services, Inc. | Callsign: Oemga Tanker, | USA | AVCODES |
| 58 | OME | Ostmecklenburgische Eisenbahngesellschaft mbH | Neubrandenburg (Connex-Gruppe > Veolia Verkehr > OLA) | D | privat-bahn.de |
| 59 | OME | Ostmecklenburgische Eisenbahn | | D | TRAFFIC |
| 60 | OMEA | OMEGA ASSOCIATES LTD | | | SCAC3 |
| 61 | OMEC | OMEGA TOOL CORP | | | SCAC4 |
| 62 | OMEG | OMEGA TRAVEL INC | | | SCAC3 |
| 63 | OMEI | OMEIR TRAVEL AGENCY | | | SCAC3 |
| 64 | OMEP | OMNI ENTERPRISES INC | | | SCAC3 |
| 65 | OMET | OKON METALS INCORPORATED | | | SCAC4 |
| 66 | OMEU | ODOM MARITIME ENTERPRISES | | | SCAC3 |
| 67 | OMF | Omniflys, S.A. de C.V. | Callsign: Omniflys, | MEX | AVCODES |
| 68 | OMF | Omniflys | | | ICAO1 |
| 69 | OMFB | OMNI FREIGHT BROKERS INC | | | SCAC3 |
| 70 | OMFI | ONEIDA MOTOR FREIGHT INC | | | SCAC4 |
| 71 | OMG | Aeromega Ltd. | Callsign: Omega, | GB | AVCODES |
| 72 | OMG | Aeromega | | | ICAO1 |
| 73 | OMGA | OMEGA PLANTATION | | | SCAC3 |
| 74 | OMGB | ONESTOP MEDIA GROUP | | | SCAC4 |
| 75 | OMGF | OMEGA FORWARDERS INC | | | SCAC3 |
| 76 | OMGG | OMEGA TRUCKING INC | | | SCAC4 |
| 77 | OMGI | OFFICE MAGIC INC | | | SCAC4 |
| 78 | OMGL | OMEGA LEASING SERVICES INC | | | SCAC4 |
| 79 | OMGM | OCEANSTAR MANAGEMENT INC | | | SCAC4 |
| 80 | OMGT | OMEGA ALPHA TRANSPORT INC | | | SCAC3 |
| 81 | OMHE | OSBORNES MOBILE HOMES | | | SCAC4 |
| 82 | OMHL | OMAHAUL INC | | | SCAC3 |
| 83 | OMHS | ORVILLES MOBILE HOME SERVICE INC | | | SCAC3 |
| 84 | OMHU | ECONOMTRADE LLC | | RUS | BIC |
| 85 | OMI | Omni Taxi Aereo S.A. | Callsign: Omni Air, | BR | AVCODES |
| 86 | OMI | Ohmi Railroad Co., Ltd. | Subsidiary of the Seibu Railway Co. Ltd. | J | TRAFFIC |
| 87 | OMIA | OIL MAN INC, THE | | | SCAC4 |
| 88 | OMIC | OMI CORP | | | SCAC3 |
| 89 | OMID | Ontario Midland R.R. Corp. | added 1/1980; 1/1980-7/2000; eliminated 4/2005; 7/2005 | | NAKINA |
| 90 | OMID | Ontario Midland R.R. Corp. | added 1/80; 1/80-7/2000 | | NRHS |
| 91 | OMID | ONTARIO MIDLAND RAILROAD CORP. | | | PWRC |
| 92 | OMID | Ontario Midland Railroad | | | RSRV |
| 93 | OMID | ONTARIO MIDLAND RAILROAD CORPORATIO | | | SCAC3 |
| 94 | OMID | Ontario Midland Railroad Corporation | | CDN | TRAFFIC |
| 95 | OMIE | OPEN MILE INC | | | SCAC4 |
| 96 | OMIH | ORITT, MICHAEL | | | SCAC4 |
| 97 | OMIL | OMI PETROLINK CORP | | | SCAC3 |
| 98 | OMIL | OMI PETROLINK CORP | | | SCAC4 |
| 99 | OMIQ | OCEANVIEW-MERCED-INGLESIDE TRUCKING | | | SCAC3 |
| 100 | OMIQ | OMEGA MANAGEMENT INC | | | SCAC4 |
