 | Off Road Challenge | 1997 | Midway | offroadc | Driving / Race (chase view) | 8.67 |
 | Off the Wall (2-player cocktail) (clone of: offtwall) | 1991 | Atari Games | offtwalc | Breakout | 0.00 |
| Off the Wall (2/3-player upright) | 1991 | Atari Games | offtwall | Breakout | 0.00 |
 | Off the Wall (Sente) | 1984 | Bally/Sente | otwalls | Sports / Tennis | 10.00 |
 | Oh My God! (Japan) | 1993 | Atlus | ohmygod | Puzzle / Drop | 0.00 |
 | Ohgon no Siro (Japan) (clone of: gladiatr) | 1986 | Taito Corporation | ogonsiro | Fighter / 2D | 0.00 |
 | Oigas (bootleg) (clone of: gigasb) | 1986 | bootleg | oigas | Breakout | 0.00 |
 | Oishii Puzzle Ha Irimasenka | 1993 | Sunsoft + Atlus | oisipuzl | Mini-Games | 10.00 |
 | Ojanko Club (Japan) | 1986 | V-System Co. | ojankoc | Tabletop / Mahjong *Mature* | 0.00 |
 | Ojanko High School (Japan) | 1988 | V-System Co. | ojankohs | Tabletop / Mahjong *Mature* | 0.00 |
 | Ojanko Yakata (Japan) | 1986 | V-System Co. | ojankoy | Tabletop / Mahjong *Mature* | 0.00 |
 | Ojanko Yakata 2bankan (Japan) | 1987 | V-System Co. | ojanko2 | Tabletop / Mahjong *Mature* | 0.00 |
 | Ojousan (Japan 871204) | 1987 | Nichibutsu | ojousan | Tabletop / Mahjong *Mature* | 0.00 |
| Ojousan [BET] (Japan 870108) (clone of: ojousan) | 1987 | Nichibutsu | ojousanm | Tabletop / Mahjong *Mature* | 0.00 |
 | Oli-Boo-Chu | 1981 | Irem + GDI | olibochu | Maze | 0.00 |
 | Olympic Soccer '92 (clone of: cupsoc) | 1992 | Seibu | olysoc92 | Sports / Soccer | 0.00 |
 | Omega (clone of: theend) | 0 | bootleg? | omega | Shooter / Gallery | 0.00 |
 | Omega Fighter | 1989 | UPL | omegaf | Shooter / Flying Vertical | 6.50 |
| Omega Fighter Special (clone of: omegaf) | 1989 | UPL | omegafs | Shooter / Flying Vertical | 0.00 |
 | Omega Race | 1981 | Midway | omegrace | Shooter / Field | 7.33 |
