Football referees
Ola Hobber Nilsen
Oskar Nilsson
Olvin Oliva
Oleksandr Omelchenko
Omar Oporto
Özer Özden
Onur Özütoprak
Onur Özütoprak
Ömər Paşayev
Oleksandr Pavlyuk
Ondřej Pechanec
O. Pelikán
Osvaldas Pliuškys
Omar Andrés Ponce Manzo
Orlando Quintana
Olani Qwinda
Oliver Raudsepp
Oliver Reitala
Olatz Rivera Olmedo
Ovidiu Robu
Óscar Rojas
Oleksandr Sakhno
Omar Sallah
Onur Sekman
Özgür Sevinç
Oleksandr Shandor
Oliver Skaret Barsøe
Ole Andreas Skogsrud Haukåsen
Oleg Snegirev
Olsi Sokoli
Oleg Sokolov
Oleksandr Solovyan
Oleg Stoianov
Oktay Taş
Olga Tereshko
O. P Thakur
Olivier Thual
Olivia Tschon
Oscar Tsotetsi
Oskari Tuomi
Özguç Türkalp
Olim Tuychibaev
Oleksandr Tytov
O. Uğurlu
Oliver Väät
Ognjen Valjić
Oscar van Hoof
Odanel Velez
Oliver Amet Vergara Rodriguez
Özgür Yankaya