| Airline |
IATA code |
ICAO code |
Logo & link |
1 Time (stop 2012)  |
T6 |
RNX |
 |
Oasis Hong Kong Airlines (stop 2008)  |
O8 |
OHK |
 |
OFD Ostfriesischer-Flug-Dienst (start 2011)  |
- |
- |
 |
Okay Airways (start 2004)  |
BK |
OKA |
 |
OKI Air International (start 1993)  |
- |
- |
 |
| Olt Express Germany (stop 2013) |
OL |
OLT |
 |
Olt Express Poland (stop 2013)  |
O2 |
JEA |
 |
Olympic Air (start 2009)  |
OA |
OAL |
 |
| Olympus Airways (start 2015) |
- |
OLY |
 |
Oman Air (start 1993)  |
WY |
OMA |
 |
Omni Air International (start 1993)  |
OY |
OAE |
 |
Omni Aviação e Tecnologia (start 1988)  |
OC |
OAV |
 |
On Air (stop 2012)  |
- |
- |
 |
One Caribbean (start ????)  |
CO |
VCY |
 |
| One Two Three Airlines (stop 2024) |
MU |
OTT |
 |
Onur Air (stop 2021)  |
8Q |
OHY |
 |
OpenSkies (stop 2020)  |
EC |
BOS |
 |
Opera Jet (stop 2014)  |
- |
- |
 |
| Orange2Fly (stop 2021) |
O4 |
OTF |
 |
Orange Air (stop 2017)  |
00 |
ORE |
 |
| Orange Air (start 2014) |
- |
ORN |
 |
| Orbest (start 2007) |
6O |
OBS |
 |
Orbest Orizonia Airlines (stop 2013)  |
40 |
IWD |
 |
Orenair (stop 2016)>>>Rossiya  |
R2 |
ORB |
 |
Orient Thai Airlines (stop 2018)  |
OX |
OEA |
 |
Oriental Air Bridge (start 1961)  |
- |
NGK |
 |
Originair (start 2015)  |
OG |
OGN |
 |
Our Airline - Nauru Airlines (start 1969)  |
ON |
RON |
 |
Overland Airways (start 2002)  |
OJ |
OLA |
 |
OWG (Off We Go)(start 2020)  |
N5 |
NRL |
 |
