Fighters — O

Jake O'Brien "Irish"

4-3 Light Heavyweight

TJ O'Brien "The Spider"

0-2 Lightweight

Sean O'Connell "The Real OC"

2-5 Light Heavyweight

Sean O'Malley "Suga"

12-3-1 Bantamweight

Chuck O'Neil "Cold Steel"

0-1 Welterweight

Casey O'Neill "King"

6-2 Women's Flyweight

Brendan O'Reilly "Badger"

1-3 Lightweight

Jose Ochoa "Kalzifer"

2-2 Flyweight

Volkan Oezdemir "No Time"

9-7 Light Heavyweight

Kaan Ofli "Genghis"

3-2 Featherweight

Trey Ogden "Shamurai"

3-3-1 Lightweight

Andy Ogle "The Little Axe"

1-5 Featherweight

Koji Oishi

0-2 Welterweight

Yushin Okami "Thunder"

14-7 Welterweight

Bolaji Oki "The Zulu Warrior"

2-3 Lightweight

Aleksei Oleinik "The Boa Constrictor"

9-8 Heavyweight

Cezary Oleksiejczuk

1-0 Middleweight

Michal Oleksiejczuk "Hussar"

10-8-1 Middleweight

Alex Oliveira "Cowboy"

11-10-1 Welterweight

Charles Oliveira "Do Bronxs"

25-11-1 Lightweight

Edilberto de Oliveira "Crocota"

0-2 Welterweight

Ednaldo Oliveira "Lula"

0-2 Light Heavyweight

Jorge de Oliveira "Blade"

0-2 Lightweight

Maria Oliveira "Spider-Girl"

1-3 Women's Strawweight

Rafaello Oliveira "Tractor"

2-6 Lightweight

Ravena Oliveira "Kenoudy"

0-3 Women's Strawweight

Saimon Oliveira

0-4 Bantamweight

Vinicius Oliveira "LokDog"

5-1 Featherweight

Felipe Olivieri

0-1 Lightweight

Gadzhi Omargadzhiev

0-2 Welterweight

Alan Omer

0-2 Featherweight

Daniel Omielanczuk

4-5 Heavyweight

Michihiro Omigawa

1-6 Featherweight

David Onama

6-3 Featherweight

Charlie Ontiveros "American Bad Boy"

0-3 Lightweight

Myktybek Orolbai

5-1 Welterweight

Brian Ortega "T-City"

8-5-1 Catch Weight

Dustin Ortiz

8-6 Flyweight

Tito Ortiz "The People's Champ"

15-11-1 Light Heavyweight

Ode Osbourne "The Jamaican Sensation"

5-8 Flyweight

Nick Osipczak

2-3 Welterweight

Nissen Osterneck

0-1 Middleweight

Rachael Ostovich

1-3 Women's Flyweight

Zak Ottow "The Barbarian"

4-4 Welterweight

Alistair Overeem "The Demolition Man"

12-8 Heavyweight

Alptekin Ozkilic "The Turkish Delight"

1-3 Flyweight