Tous les combattants
 | Oscar Jurado Sanchez | 2-0-0 REC | #439 |  |
 | Oscar Mendez | 0-1-0 REC | #5141 |  |
 | Oscar Miguel | #7935 |  | |
 | Oscar Ownsworth | 2-3-0 REC | #799 |  |
 | Oscar Ravello | #8080 | | |
 | Oseas Cruz Furtado | 0-1-0 REC | #8001 |  |
 | Oseyiomon Oiyemhonlan | 1-2-0 REC | #4837 | |
 | Osimkhon Rakhmonov | 3-1-0 REC | #440 |  |
 | Oskar Piechota | 2-3-0, 1NC UFC | #3821 |  |
 | Oskar Stachura | 1-1-0 REC | #790 | |
 | Oskar Staszczak | 1-0-0 REC | #2583 | |
 | Oskar Szczepaniak | 4-2-0 REC | #3005 | |
 | Osman Minbatirov | 1-1-0 REC | #6029 |  |
 | Osvaldo Benedito | 0-1-0 REC | #5190 |  |
 | Otabek Rajabov | 1-0-0 REC | #3581 | |
 | Otar Tanzilov | 0-1-0 REC | #4930 |  |
 | Otari Tanzilovi | 0-1-0 UFC | #3813 | |
 | Otgonbaatar Boldbaatar | 0-1-0 REC | #5775 |  |
 | Oton Jasse | 0-3-0 REC | #4394 | |
 | Ottman Azaitar | 2-3-0 UFC | #1885 |  |
 | Otto Rodrigues | 1-1-0 REC | #6616 | |
 | Oualy Tandia | 1-0-0 REC | #899 |  |
 | Oumar Kane | 1-0-0 REC | #3074 |  |
 | Oumar Sy | 3-2-0 UFC | #357 | |
 | Ourouzmag Magkeyev | 0-1-0 REC | #4410 | |