Tous les combattants
 | Osimkhon Rakhmonov | 2-1-0 REC | #2569 |  |
 | Oskar Piechota | 2-3-0, 1NC UFC | #3799 |  |
 | Oskar Stachura | 1-1-0 REC | #630 | |
 | Oskar Staszczak | 1-0-0 REC | #2488 | |
 | Oskar Szczepaniak | 4-2-0 REC | #3000 | |
 | Osman Minbatirov | 1-1-0 REC | #5947 |  |
 | Osvaldo Benedito | 0-1-0 REC | #5210 |  |
 | Otabek Rajabov | 1-0-0 REC | #3527 | |
 | Otar Tanzilov | 0-1-0 REC | #4923 |  |
 | Otari Tanzilovi | 0-1-0 UFC | #3981 | |
 | Otgonbaatar Boldbaatar | 0-1-0 REC | #5683 |  |
 | Oton Jasse | 0-3-0 REC | #4337 |  |
 | Ottman Azaitar | 2-3-0 UFC | #1911 |  |
 | Otto Rodrigues | 1-1-0 REC | #6590 | |
 | Oualy Tandia | 1-0-0 REC | #788 |  |
 | Oumar Kane | 1-0-0 REC | #3005 |  |
 | Oumar Sy | 3-2-0 UFC | #370 | |
 | Ourouzmag Magkeyev | 0-1-0 REC | #4413 | |
 | Ousmane Camara | 1-0-0 REC | #1392 | |
 | Ovidio Bojorquez | 0-1-0 REC | #7017 |  |
 | Ovince St. Preux | 15-13-0 UFC | #283 |  |
 | Owain Williams | 0-1-0 REC | #7104 |  |
 | Owen Jason | 1-0-0 REC | #7829 | |
 | Oyatullo Muminov | 2-1-0 REC | #1249 | |
 | Ozan Aslaner | 3-2-0 REC | #1281 |  |