Tous les combattants
 | Ode Osbourne | 5-7-0, 1NC UFC | #962 |  |
 | Oganes Voskanyan | 1-2-0 REC | #2337 |  |
 | Ognjen Dimic | 0-3-0 REC | #3465 |  |
 | Ole Hetleflat | 1-0-0 REC | #2323 |  |
 | Ole Magnor | 2-2-0 REC | #4485 | |
 | Oleg Borisov | 2-1-0 REC | #2445 | |
 | Oleg Dadonov | 1-1-0 REC | #1844 | |
 | Oleg Nagorny | 0-1-0 REC | #7457 |  |
 | Oleg Olenichev | 0-1-0 REC | #5823 | |
 | Oleg Popov | 7-1-0 REC | #1073 | |
 | Oleg Taktarov | 6-2-1 UFC | #1852 | |
 | Oļegs Jemeļjanovs | 0-2-0 REC | #5970 |  |
 | Oleksandr Moisa | 2-1-0 REC | #995 | |
 | Oleksii Polischuck | 4-4-0 REC | #1673 | |
 | Olena Kolesnyk | 4-4-0 REC | #3300 | |
 | Olendet Apouassa Romeo | 0-1-0 REC | #5760 |  |
 | Olga Rubin | 4-3-0 REC | #2114 | |
 | Oli Thompson | 0-2-0 UFC | #5223 |  |
 | Oliver Enkamp | 0-2-0 UFC | #3757 |  |
 | Oliver Tero | 1-1-0 REC | #1896 | |
 | Olivia Hendrickson | 1-0-0 REC | #4952 | |
 | Olivia Parker | 0-1-0 REC | #5216 | |
 | Olivier Aubin-Mercier | 7-5-0 UFC | #180 |  |
 | Olivier Fleurmon | 1-0-0 REC | #1971 |  |
 | Olivier Murad | 1-0-0 REC | #5439 |  |