Tous les combattants
 | Olli Santalahti | 2-3-0 REC | #3471 |  |
 | Ollie Sarwa | 5-1-0 REC | #272 |  |
 | Ollie Schmid | 0-1-0 UFC | #3171 |  |
 | Olutobi Kalejaiye | 1-1-0 REC | #1389 |  |
 | Oluwale Bamgbose | 1-4-0 UFC | #3578 |  |
 | Omar Amasha | #7680 |  | |
 | Omar El Bily | 0-1-0 REC | #5950 |  |
 | Omar El Dafrawy | 5-1-0 REC | #638 | |
 | Omar Hussein | 0-2-0 REC | #3739 |  |
 | Omar Morales | 3-4-0 UFC | #2517 |  |
 | Omar Reguigui | 0-1-0, 1NC REC | #4587 |  |
 | Omar Santana | 0-1-0 REC | #7293 |  |
 | Omar Tugarev | 0-2-0 REC | #4263 | |
 | Omari Akhmedov | 9-5-1 UFC | #593 |  |
 | Omiel Brown | 9-3-0 REC | #388 | |
 | Omoyele Gonzalez | 0-1-0 REC | #5741 | |
 | Omran Chaaban | 3-0-0 REC | #965 | |
 | Onassis Parungao | 1-0-0 UFC | #6183 |  |
 | Ondrej Petrasek | 1-1-0 REC | #6722 |  |
 | Ondrej Raska | 4-3-0 REC | #1321 | |
 | Orion Cosce | 1-2-0 UFC | #3988 | |
 | Orlando Sanders | 0-1-0 REC | #7427 | |
 | Orlando Wiet | 1-1-0 UFC | #3087 |  |
 | Orlando Wilson Prins | 2-4-0 REC | #3192 | |
 | Ornella Vivaldi | 0-1-0 REC | #7853 | |