| Title | Year | Genre |
|---|---|---|
| Operation Combat II | ???? | Management |
| Operation Desert Storm | 1994 | Action |
| Operation Firestorm | 1993 | Action |
| Operation Harrier | ???? | Action |
| Operation Jupiter | ???? | Action |
| Operation Lemming | ???? | Arcade |
| Operation Neptune | 1989 | Action |
| Operation Overlord - The Invasion of Europe | ???? | Strategy |
| Operation Stealth | ???? | Adventure |
| Operation Thunderbolt | ???? | Gun shooter |
| Operation Wolf | ???? | Gun shooter |
| Opposites Attract | ???? | Educational |
| Oracle Horse Racing System | 1991 | Management |
| Orb | 1994 | Puzzle |
| Orbit | 1994 | Arcade |
| Orbit 2000 | 1991 | Shooter |
| Oriental Games | ???? | Adventure |
| Ork | ???? | Platform |
| Ork Attack The Return | ???? | Arcade |
| Ortho-CM | ???? | Educational |
| Orthogus Tome 1 | ???? | Educational |
| Ortotris | 1994 | Puzzle |
| Oscar | ???? | Platform |
| Osiris | ???? | Puzzle |
| Oswald | ???? | Arcade |
| OsWALD of the Ice Floes | ???? | Arcade |
| Othello Killer | 1989 | Puzzle |
| Otik Gold Edice | ???? | Adventure |
| Out of this World | ???? | Adventure |
| Out Run | 1989 | Racing |
| Out Run Europa | ???? | Moto racing |
| Out to Lunch | ???? | Platform |
| Outerim | ???? | Management |
| Outfall | 1995 | Puzzle |
| Outlands | ???? | Shooter |
| Outliner | 1996 | Shooter |
| Outpost - Solo Assault | 1991 | Spaceship |
| Outzone | ???? | Shooter |
| Over the Net | ???? | Volleyball |
| Overdose | 1996 | Puzzle |
| Overdrive | ???? | Action |
| Overkill | ???? | Shooter |
| Overlander | ???? | Racing |
| Overlord | ???? | Adventure |
| Overrun! - A Tactical Game of Modern Land Warfare | ???? | Strategy |
| OverTaking | 1994 | Arcade |
| Oxxonian | ???? | Arcade |
| Oxyd | ???? | Puzzle |
| Oxyd Magnum! | 1993 | Arcade |
| Oxyd Magnum! | ???? | Arcade |
