Tous les combattants
 | Oleksii Polischuck | 4-4-0 REC | #2046 |  |
 | Olena Kolesnyk | 4-4-0 REC | #3524 | |
 | Olendet Apouassa Romeo | 0-1-0 REC | #5763 |  |
 | Olga Rubin | 4-3-0 REC | #2399 |  |
 | Oli Thompson | 0-2-0 UFC | #5222 |  |
 | Oliver Enkamp | 0-2-0 UFC | #3995 |  |
 | Oliver Tero | 2-1-0 REC | #889 | |
 | Olivia Hendrickson | 1-0-0 REC | #5150 |  |
 | Olivia Parker | 0-1-0 REC | #5337 | |
 | Olivier Aubin-Mercier | 7-5-0 UFC | #207 |  |
 | Olivier Fleurmon | 1-0-0 REC | #2452 |  |
 | Olivier Murad | 1-0-0 REC | #5923 |  |
 | Olli Santalahti | 2-3-0 REC | #3717 |  |
 | Ollie Sarwa | 5-1-0 REC | #816 | |
 | Ollie Schmid | 0-1-0 UFC | #2890 |  |
 | Olutobi Kalejaiye | 1-1-0 REC | #2070 |  |
 | Oluwale Bamgbose | 1-4-0 UFC | #3760 | |
 | Olzhas Moldagaliev | #8173 |  | |
 | Omar Amasha | #8008 |  | |
 | Omar El Bily | 0-1-0 REC | #6427 |  |
 | Omar El Dafrawy | 6-1-0 REC | #576 | |
 | Omar Hussein | 1-3-0 REC | #995 |  |
 | Omar Morales | 3-4-0 UFC | #2578 |  |
 | Omar Reguigui | 0-1-0, 1NC REC | #4887 |  |
 | Omar Santana | 0-1-0 REC | #7504 |  |