| 1 | OY | Omni Air International, Inc. d/b/a Omni Air Express | ICAO: OAE, Callsign: Omni-Express, IATA Designator changed from 1I | USA | AVCODES |
| 2 | OY | African Intercontinental Airways | Designator OY recalled by IATA | WAG | AVCODES |
| 3 | OY | Conair A/S | ICAO: OYC, Callsign: Conair, Name changed to Conair of Scandinavia | DK | AVCODES |
| 4 | OY | Oy Soder Air Ltd. | ICAO: SDE, Callsign: Soder, Designator OY recalled by IATA | FIN | AVCODES |
| 5 | OY | Andes Lineas Aereas S.A. | ICAO: ANS, Callsign: Aeroandes, Accounting code 650 recalled by IATA. Designator OY reinstated by IATA | RA | AVCODES |
| 6 | OYA | Fly OYA International Airline d/b/a FLY OYA | IATA: YI, Callsign: Oyaa, Planned startup in May 2022. | LAR | AVCODES |
| 7 | OYAC | ONTARIO YACHTS CO LTD | | | SCAC4 |
| 8 | OYC | Conair of Scandinavia | Callsign: Conair, | DK | AVCODES |
| 9 | OYC | Conair A/S | IATA: OY, Callsign: Conair, Name changed to Conair of Scandinavia | DK | AVCODES |
| 10 | OYE | Koda International Ltd. | Callsign: Koda Air, | WAN | AVCODES |
| 11 | OYE | Koda International | | | ICAO1 |
| 12 | OYEH | OYE, HERMAN L | | | SCAC3 |
| 13 | OYEI | O & Y ENTERPRISE INC | | | SCAC4 |
| 14 | OYER | OYER, INC | | | SCAC3 |
| 15 | OYGT | OLNEY, REGGIE F GENERAL TRUCKING | | | SCAC3 |
| 16 | OYGT | OESTERREICHISCHE | | | SCAC4 |
| 17 | OYLF | OYOLA, LUIS F | | | SCAC4 |
| 18 | OYLQ | OYLER MOTOR TRANSIT CO INC | | | SCAC3 |
| 19 | OYLQ | OSPREY MARINE LTD | | | SCAC4 |
| 20 | OYLR | The Olympic R.R. Co. | eliminated 7/2008 | | NAKINA |
| 21 | OYMC | OLYMPIC CARRIERS INC | | | SCAC4 |
| 22 | OYME | ONAN Y ME | | | SCAC4 |
| 23 | OYO | Oyonnair | Callsign: Rogue, | F | AVCODES |
| 24 | OYSS | ODYSSEY TRANSPORT INC | | | SCAC4 |
| 25 | OYST | OYSTER BAY MOTOR HAULAGE, INC | | | SCAC3 |
| 26 | OYTC | OLYMPIC TRANS CORP | | | SCAC4 |
| 27 | OYTG | OLYMPIC TRUCKING INC | | | SCAC3 |
| 28 | OYTG | OHIO PACKING COMPANY | | | SCAC4 |
