Airlines
| Airline Name | Country | IATA Code | ICAO | AWB Prefix |
|---|---|---|---|---|
| O?Connor Mt Gambier?s Airline | Australia | UQ | OCM | |
| OzJet | Australia | O7 | OZJ | |
| Occidental Airlines | Belgium | OCT | ||
| Okay Airways | China | BK | OKA | |
| Orbi Georgian Airlines | Georgia | NQ | DVU | 819 |
| OLT- Ostfriesische Lufttransport GmbH | Germany | OL | OLT | 704 |
| Olympic Airways | Greece | OA | OAL | 50 |
| Oasis Hong Kong Airlines | Hong Kong | O8 | OHK | |
| Ocean Airlines | Italy | VC | VCX | |
| Oriental Air Bridge | Japan | NGK | ||
| Omega Aero | Mexico | |||
| Our Airline | Nauru | ON | RON | 123 |
| Okada Air | Nigeria | 9H | OKJ | |
| Oriental Airlines | Nigeria | OAC | ||
| Oman Air | Oman | WY | OAS | 910 |
| Orbest | Portugal | 4O | OBS | |
| Omskavia | Russia | N3 | OMS | 753 |
| Orenair | Russia | R2 | ORB | 291 |
| Orient-Avia | Russia | ORT | ||
| Oriol Avia Soviet Austrian | Russia | OAU | 584 |