| 1 | OH | PSA Airlines | ICAO: JIA, Callsign: Blue Streak, Name reverted to Jetstream International Airlines. Changed name from Jetstream International Airlines w.e.f. 01 November 1995. US Airways Express Carrier | USA | AVCODES |
| 2 | OH | Comair, Inc. | ICAO: COM, Callsign: Comair, IATA Prefix: 886, Ceased operations on 29 September 2012 | USA | AVCODES |
| 3 | OH | SFO Helicopter Airlines, Inc. | Callsign: SFO Airlines, | USA | AVCODES |
| 4 | OH | XP International BV | ICAO: XPS, Callsign: XP Parcel, Ceased operations. Designator OH recalled by IATA | NL | AVCODES |
| 5 | OH | Jetstream International Airlines | ICAO: JIA, Callsign: Blue Streak, Name from PSA Airlines. Changed name from Jetstream International Airlines w.e.f. 01 November 1995. US Airways Express Carrier | USA | AVCODES |
| 6 | OHA | Air Odon | Callsign: Air Odon, | F | AVCODES |
| 7 | OHA | O.H. Aviation | | F | AVCODES |
| 8 | OHAD | OHIO AUTO DELIVERY | | | SCAC3 |
| 9 | OHAD | ORMAN BROTHERS | | | SCAC4 |
| 10 | OHAF | O H & F INC | | | SCAC3 |
| 11 | OHAJ | OHARA, J F & SON INC | | | SCAC3 |
| 12 | OHAR | OHARA CORPORATION | | | SCAC4 |
| 13 | OHAT | OCHOA'S TRUCKING | | | SCAC4 |
| 14 | OHAV | O'HARE VAN LINES, INC | | | SCAC3 |
| 15 | OHBL | OHIO BARGE LINE INC, | | | SCAC3 |
| 16 | OHBL | OHIO BARGE LINE INC, | | | SCAC4 |
| 17 | OHC | Jet Select, LLC | Callsign: Ohio-Charter, Merged into Jet Edge. | USA | AVCODES |
| 18 | OHCC | OHIO CARRIER CORPORATION | | | SCAC3 |
| 19 | OHCD | O'HARE COLD CO | | | SCAC4 |
| 20 | OHCN | OHIO CONNECTION | | | SCAC3 |
| 21 | OHCN | OHC INTERMODAL | | | SCAC4 |
| 22 | OHCR | Ohio Central R.R. Inc. | 1/1994-7/2005 | | NAKINA |
| 23 | OHCR | The Columbus & Ohio River R.R. Co. | added 10/1992 | | NAKINA |
| 24 | OHCR | Ohio R.R. System | eliminated 10/1992 | | NAKINA |
| 25 | OHCR | Ohio Central R.R. Inc. | added 7/1988; 1/1994 | | NAKINA |
| 26 | OHCR | Ohio Central R.R. Inc. | added 7/88; 1/94 | | NRHS |
| 27 | OHCR | Ohio R.R. System | eliminated 10/92 | | NRHS |
| 28 | OHCR | The Columbus & Ohio River R.R. Co. | added 10/92 | | NRHS |
| 29 | OHCR | Ohio Central R.R. Inc. | 1/94-7/2000 | | NRHS |
| 30 | OHCR | OHIO CENTRAL RAILROAD, INC. [COLUMBUS & OHIO RIVER RAILROAD CO.] | | | PWRC |
| 31 | OHCR | Ohio Central Railroad | | | RSRV |
| 32 | OHCR | OHIO CENTRAL RAILROAD CO | | | SCAC3 |
| 33 | OHCR | OHIO CENTRAL RAILROAD CO | | | SCAC4 |
| 34 | OHCR | Ohio Central Railroad Inc | | USA | TRAFFIC |
| 35 | OHCX | Stauffer Chemical Co. — Eastern Branch | added 4/1965; 7/1965 (not listed) | | NAKINA |
| 36 | OHCX | Old Hickory Chemical Co. | 7/1932-4/1961; eliminated 1/1965 | | NAKINA |
| 37 | OHCX | Old Hickory Chemical Co. | 4/38-4/61; eliminated 1/65 | | NRHS |
| 38 | OHCX | Stauffer Chemical Co. -- Eastern Branch | added 4/65; 7/65 | | NRHS |
| 39 | OHCX | STAUFFER CHEMICAL CO. - EASTERN BRANCH [OLD HICKORY CHEMICAL CO.] | | | PWRC |
| 40 | OHDI | OHIO DISPATCH INC | | | SCAC3 |
| 41 | OHDL | OMAHA DIRECT LLC | | | SCAC4 |
| 42 | OHE | Osthavelländische Eisenbahn Berlin-Spandau AG | Berlin | D | privat-bahn.de |
| 43 | OHE | Osthannoversche Eisenbahn AG | Celle | D | privat-bahn.de |
| 44 | OHE | Osthannoversche Eisenbahnen | | D | TRAFFIC |
| 45 | OHE | Osthannoversche Eisenbahnen | | DE | VKM |
| 46 | OHEE | OHIO EASTERN EXPRESS INC | | | SCAC3 |
| 47 | OHEE | OHIO EASTERN EXPRESS INC | | | SCAC4 |
| 48 | OHEGO | OHE Cargo GmbH | | DE | VKM |
| 49 | OHER | OTTERHOLE MANAGEMENT LLC | | | SCAC4 |
| 50 | OHESP | Osthavelländische Eisenbahnen Berlin-Spandau AG | Real: OHE-SP | D | TRAFFIC |
| 51 | OHFX | Fluor Daniel Fernald | 7/2000-7/2005 (not listed) | | NAKINA |
| 52 | OHFX | Fluor Daniel Fernald | Jul-00 | | NRHS |
| 53 | OHFX | FLUOR DANIEL FERNALD | | | PWRC |
| 54 | OHFX | Fluor Daniel Fernald | | | RSRV |
| 55 | OHFX | US DEPARTMENT OF ENERGY EM CONSOLID | | | SCAC4 |
| 56 | OHGI | OLLENDORFF, H G INC | | | SCAC3 |
| 57 | OHGI | OCHOA GONZALEZ, RODRIGO | | | SCAC4 |
| 58 | OHGR | OLIVARES HERNANDEZ GONZALO, RAUL | | | SCAC4 |
| 59 | OHGX | Otha H. Grimes (Grimes Gasoline Co.) | 7/1937-4/1938; 1/1943-7/1954 | | NAKINA |
| 60 | OHGX | Otha H. Grimes | 7/1930-7/1935 | | NAKINA |
| 61 | OHGX | Otha H. Grimes | Apr-38 | | NRHS |
| 62 | OHGX | Otha H. Grimes (Grimes Gasoline Co.) | Jan-52 | | NRHS |
| 63 | OHGX | GRIMES GASOLINE CO. [OTHA H. GRIMES] | | | PWRC |
| 64 | OHHG | OLINGER HEAVY HAULING | | | SCAC4 |
| 65 | OHHL | O H HUNT LINE INC | | | SCAC3 |
| 66 | OHIC | Ohi-Rail Corp. | added 10/1982; eliminated 10/1987; eliminated 1/1991; 1/1994-7/2005 | | NAKINA |
| 67 | OHIC | Ohi-Rail Corp. | added 10/82; eliminated 10/87; eliminated 1/91; 1/94-7/2000 | | NRHS |
| 68 | OHIC | OHI-RAIL CORPORATION | | | PWRC |
| 69 | OHIC | Ohi-Rail Corporation | | | RSRV |
| 70 | OHIC | OHI-RAIL CORPORATION | | | SCAC3 |
| 71 | OHIE | OHIO INTRA EXPRESS INC | | | SCAC3 |
| 72 | OHIE | OHIO INTRA EXPRESS INC | | | SCAC4 |
| 73 | OHIQ | OHIO TRANSFER INC | | | SCAC3 |
| 74 | OHJ | Odsherred Jernbane (Odsherredsbanen) | 1899 - 2003 | DK | jernbanen.dk |
| 75 | OHJ | Orsa - Härjedalen Järnväg | 1908 - 1919 | S | svenska-lok.se |
| 76 | OHJ | Odsherred Jernbane (Odsherredsbanen) | 1899 - 2003 | DK | TRAFFIC |
| 77 | OHK | Oasis Hong Kong Airlines Limited | IATA: O8, Callsign: Oasis, IATA Prefix: 558, Ceased Operations | HK | AVCODES |
| 78 | OHK | Oasis Hong Kong Airlines | IATA: O8 | | ICAO1 |
| 79 | OHK | Oasis Hong Kong Airlines | | HK | TRAFFIC |
| 80 | OHKU | TOK AMERICA | | USA | BIC |
| 81 | OHKU | OHKA AMERICAN INCORPORATED USA | | | PWRC |
| 82 | OHKU | Ohka American | | | RSRV |
| 83 | OHKY | OHIO-KENTUCKY STEEL CORP | | | SCAC3 |
| 84 | OHLB | OHL BROTHERS FARMS | | | SCAC3 |
| 85 | OHLC | OHLCO INC | | | SCAC4 |
| 86 | OHLD | OHL DISTRIBUTING | | | SCAC4 |
| 87 | OHLO | OHIO LOGISTICS | | | SCAC4 |
| 88 | OHLR | OHLERS TOWING SERVICE | | | SCAC3 |
| 89 | OHLR | O'HALLORAN, P E INC | | | SCAC4 |
| 90 | OHLT | OHL DISTRIBUTING (REFRIGERATED) | | | SCAC4 |
| 91 | OHLY | OHLEY TRANSFER COMPANY | | | SCAC3 |
| 92 | OHMC | OHM CYCLES LTD | | | SCAC4 |
| 93 | OHMI | ONE HOUR MESSENGER INC | | | SCAC4 |
| 94 | OHMK | O H MELING TANKERS KS | | | SCAC4 |
| 95 | OHMS | OLIVE HILL MOTOR SALES INC | | | SCAC3 |
| 96 | OHMT | OHIO MOBILE TRANSPORT | | | SCAC3 |
| 97 | OHMV | OLD HARBOR MOVING & STORAGE INC | | | SCAC3 |
| 98 | OHNT | OHIO NORTHERN TRANSIT CO | | | SCAC3 |
| 99 | OHNT | OHIO NORTHERN TRANSIT CO | | | SCAC4 |
| 100 | OHOX | U.S. Dept. of Energy Ohio Field | 7/2000-7/2005 (not listed) | | NAKINA |
