Tous les combattants
 | Oban Elliott | 3-2-0 UFC | #1343 |  |
 | Oceane Samson | 2-0-0 REC | #1198 |  |
 | Ode Osbourne | 5-7-0, 1NC UFC | #973 |  |
 | Oganes Voskanyan | 1-2-0 REC | #2402 |  |
 | Ognjen Dimic | 0-3-0 REC | #3511 |  |
 | Ole Hetleflat | 1-0-0 REC | #2394 |  |
 | Ole Magnor | 2-2-0 REC | #4519 | |
 | Oleg Borisov | 2-1-0 REC | #2515 | |
 | Oleg Dadonov | 1-1-0 REC | #1914 | |
 | Oleg Nagorny | 0-1-0 REC | #7468 |  |
 | Oleg Olenichev | 0-1-0 REC | #5846 | |
 | Oleg Popov | 7-1-0 REC | #1082 | |
 | Oleg Taktarov | 6-2-1 UFC | #1851 | |
 | Oļegs Jemeļjanovs | 0-2-0 REC | #6041 |  |
 | Oleksandr Moisa | 2-1-0 REC | #1066 | |
 | Oleksii Polischuck | 4-4-0 REC | #1706 | |
 | Olena Kolesnyk | 4-4-0 REC | #3333 | |
 | Olendet Apouassa Romeo | 0-1-0 REC | #5788 |  |
 | Olga Rubin | 4-3-0 REC | #2173 | |
 | Oli Thompson | 0-2-0 UFC | #5204 |  |
 | Oliver Enkamp | 0-2-0 UFC | #3774 |  |
 | Oliver Tero | 1-1-0 REC | #1968 | |
 | Olivia Hendrickson | 1-0-0 REC | #5032 | |
 | Olivia Parker | 0-1-0 REC | #5287 | |
 | Olivier Aubin-Mercier | 7-5-0 UFC | #185 |  |