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| 18 Compagnies | Compagnie (100) | Nb | Co | Nation | Notes |
| Oasis International Airlines | Oasis International Airlines | 23 | 0 | Espagne | Faillite |
| Okay Airways | Okay Airways | 27 | 10 | Chine | |
| OLT Express (Escroquerie) | OLT Express | 15 | 0 | Pologne | Faillite |
| Octavia Airlines | Octavia Airlines | 9 | 0 | France | Fermé |
| Olympic Air | Olympic Air | 18 | 0 | Grèce | |
| Ostfriesische Lufttransport | Ostfriesische Lufttransport | 13 | 0 | Allemagne | Fermé |
| Oman Air | Oman Air | 35 | 12 | Oman | |
| Omskavia Airlines | Omskavia Airlines | 10 | 0 | Russie | Fermé |
| One Air | One Air | 4 | 1 | UK | Cargo |
| One-Two-Go Airlines § | One-Two-Go Airlines | 17 | 0 | Thaïlande (Accident) | Liquidé |
| OpenSkies | OpenSkies | 4 | 3 | France | Fermé |
| Orbis | Orbis | 1 | 0 | Ghana | Humanitaire |
| Orenair | Orenair | 26 | 4 | Russie | |
| Orion Airways | Orion Airways | 21 | 0 | UK | Fusionné |
| Overseas National Air. | Overseas Natio. Air. | 82 | 0 | USA | Fermé |
| OWG | OWG | 4 | 1 | Canada | |
| Ozark Airlines | Ozark Airlines | 128 | 0 | USA | Fusionné |
| PAL Airlines | PAL Airlines | 13 | 0 | Chili | Faillite |
| PAL Express | PAL Express | 27 | 5 | Philippines |
§ Mépris flagrant de la sécurité
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