Tous les combattants
 | 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 | |
 | Oron Kahlon | 0-1-0 REC | #5475 |  |
 | Ortsa Gudaev | 1-1-0 REC | #5053 | |
 | Osama Elsaidy | 0-1-0 REC | #7127 | |
 | Oscar Jurado Sanchez | 1-0-0 REC | #1176 | |
 | Oscar Mendez | 0-1-0 REC | #5204 | |
 | Oscar Miguel | #7757 |  | |
 | Oscar Ownsworth | 1-3-0 REC | #3477 | |