Games starting with letter O
N64
Genesis 
SNES
NES
Sega
Omega Race
Onslaught
Olympic Gold - Barcelona 92
Olympic Winter Games - Lillehammer 94
Obitus
Ogre Battle
Olympic Summer Games
On the Ball
Off Road Challenge
Ogre Battle 64: Person of Lordly Caliber
Olympic Hockey Nagano '98
Olympic Gold
Oddworld: Munch's Oddysee
One Piece
Oddworld Abes Exoddus
Oddworld Abes Oddysee
O.D.T.
Onimusha Warlords
Obsidian
Odium
Of Light and Darkness: The Prophecy
Ominous Horizons: A Paladin's Calling 
Oni
Odama
Obscure
Oddworld: Stranger's Wrath
Okage: Shadow King
Okami
Onimusha 2: Samurai's Destiny
Onimusha 3: Demon Siege
Onimusha Blade Warriors
Onimusha: Dawn of Dreams
Omega Boost
Online Chess Kingdoms
Ooga Booga
Ogre Battle 64
Oddworld Adventures
Olympic Summer Games: Atlanta 1996
Oddworld Adventures 2
Onimusha 3