- Octavio MarettoPosition: shooting guardNationality: Italy, Argentina
- Octavio VidalesBorn: April 2, 1965Sport: association football
- Odalys RivasPosition: midfielder, defenderBorn: October 9, 1998
- Olbis Futo AndrèPosition: centerNationality: Angola, Italy
- Olienka SalinasPosition: forwardBorn: November 16, 1973
- Oliver RiveraPosition: centre-backBorn: March 7, 2002
- Olivia OstoniNationality: ItalyBorn: May 13, 2007
- Omar CuyaPosition: defenderBorn: September 2, 1981
- Omar DiengNationality: ItalyBorn: February 17, 2000
- Omar KaremPosition: point guardNationality: Italy, Morocco
- Omar MaininiNationality: ItalyBorn: October 3, 2006
- Omar ReyesPosition: midfielderBorn: December 13, 1988
- Omar ZegarraPosition: defenderBorn: August 6, 1980
- Orazio SapienzaNationality: ItalyBorn: December 16, 1994
- Orestes JordánPosition: defenderBorn: November 21, 1913
- Oriana MilazzoPosition: point guardNationality: Italy
- Orlando AllendePosition: forwardBorn: January 9, 1988
- Orlando Contreras CollantesPosition: sweeper, centre-backBorn: June 1982
- Orlando de la TorrePosition: defenderBorn: November 21, 1943
- Orlando MendutoNationality: ItalyBorn: January 18, 1976
- Orlando PradoPosition: defenderBorn: February 16, 1972
- Orlando TournPosition: center, power forwardNationality: Italy, Argentina
- Oscar AlbuquerquePosition: midfielderBorn: September 4, 1954
- Oscar MensahNationality: ItalyBorn: January 27, 2000
- Oscar VílchezPosition: midfielderBorn: January 21, 1986
- Oslimg MoraPosition: wing halfBorn: June 2, 1999
- Osnar NoronhaPosition: forwardBorn: December 17, 1991
- Osondu James ForchettaNationality: ItalyBorn: February 10, 2009
- Oswaldo AraujoPosition: forwardBorn: October 3, 1964
- Oswaldo CarriónPosition: defenderBorn: May 31, 1980
- Oswaldo RamírezPosition: forwardBorn: March 28, 1947
- Otis RealeNationality: ItalyBorn: October 16, 1998
- Ottorino SartorPosition: goalkeeperBorn: September 18, 1945
- Óscar ArizagaPosition: defenderBorn: August 20, 1957
- Óscar Gómez SánchezPosition: forwardBorn: October 31, 1934
- Óscar MontalvoPosition: midfielderBorn: March 20, 1937
- Óscar OxleyPosition: goalkeeperBorn: 1914
- Óscar PintoPosition: midfielderBorn: January 20, 2002
- Óscar Vega GuerreroPosition: midfielderBorn: March 25, 1989