 | Oedo Fight (Japan Bloodshed Ver.) (clone of: bloodwar) | 1994 | Kaneko | oedfight | | 0.00 |
 | Off Road Challenge (v1.10) (clone of: offroadc) | 1997 | Midway | offroadc1 | | 0.00 |
| Off Road Challenge (v1.30) (clone of: offroadc) | 1997 | Midway | offroadc3 | | 0.00 |
| Off Road Challenge (v1.40) (clone of: offroadc) | 1997 | Midway | offroadc4 | | 0.00 |
| Off Road Challenge (v1.63) | 1997 | Midway | offroadc | Driving / Race (chase view) | 9.00 |
 | Off the Wall (2-player cocktail) (clone of: offtwall) | 1991 | Atari Games | offtwallc | | 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 | 8.45 |
| | Office Yeo In Cheon Ha (version 1.2) | 2001 | Danbi | officeye | | 0.00 |
 | Oh My God! (Japan) | 1993 | Atlus | ohmygod | Puzzle / Drop | 9.00 |
| | Oh! Paipee (Japan 890227) | 1989 | Nichibutsu | ohpaipee | | 0.00 |
 | Ohgon no Siro (Japan) (clone of: gladiatr) | 1986 | Taito Corporation | ogonsiro | Fighter / 2D | 0.00 |
| | Oigas (bootleg) (clone of: gigas) | 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* | 3.00 |
 | 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 |
