Orkhan Abdulov vs Gadir Guseinov
Dubai Open Dubai UAE round 4 2010.04.08
Sicilian Defense: Classical Variation 0-1

Oscar Chajes vs David Janowski
Rice Memorial New York, NY USA round 5 1916.01.23
Döry Defense 1/2-1/2

Oscar Panno vs Alfredo Olivera
Mar del Plata Mar del Plata ARG round 2 1958.03.12
Queen’s Gambit Declined: Alapin Variation 1-0

Oscar Quinones Carrillo vs Vasily Smyslov
Amsterdam Interzonal Amsterdam NED round 1 1964.05.20
Pirc Defense: Austrian Attack 0-1

Oskar Antze vs Carl Hartlaub
Match 1909/11 Bremen GER round 14 1911.06.28
English Opening: King’s English Variation 1-0

Oskar von Bahr vs Florian Handke
32nd Rilton Cup Stockholm SWE round 7 2003.01.03
French Defense: Winawer Variation, Advance Variation 1-0

Ossip Bernstein vs Benjamin Leussen
DSB-13.Kongress Hauptturnier A Hannover GER round 7 1902.??.??
Ruy Lopez: Exchange Variation, Alapin Gambit 1-0

Otto B Morcken vs Fernand Morel
Helsinki ol (Men) fin-C Helsinki FIN round 2 1952.08.22
Grünfeld Defense: Counterthrust Variation 0-1

Ovidiu-Doru Foisor vs Sergey Borisovich Smagin
Nimes op Nimes round 2 1991.??.??
Nimzo-Indian Defense: Classical Variation 1-0

Owen M Hindle vs Raymond Keene
Stevenson Memorial Bognor Regis (ENG) round 8 1964.04.08
Caro-Kann Defense: Classical Variation 1/2-1/2