| Game Name | System |
|---|
| Onslaught (1989)(Realms)[cr Quant] | Atari ST |
| Ontama - Onpu-tou Hen (J)(Sir VG) | NDS |
| Ontamarama (U)(XenoPhobia) | NDS |
| Onyanko Town (Japan) | NES |
| Onyx | Atari 800 |
| Onyx (Brazil/Prototype) | MAME |
| Oo Topos (1986)(Polarware Penguin Software Inc) | DOS |
| Oo-Topos | Amiga |
| Oo-Topos (1984)(Polarware - Penguin Software)[cr](Disk 1 of 1 Side A) | Apple2 |
| Oo-Topos (1984)(Polarware - Penguin Software)[cr](Disk 1 of 1 Side B) | Apple2 |
| Oo-Topos (1986)(Softkill Int.) | Atari ST |
| OoEdo Renaissance - Pack in Video (J) | Saturn |
| Ooedo Hanseiki (19xx)(Panther Software)(Disk 1 of 3) | X68K |
| Ooedo Hanseiki (19xx)(Panther Software)(Disk 2 of 3) | X68K |
| Ooedo Hanseiki (19xx)(Panther Software)(Disk 3 of 3) | X68K |
| Ooedo Huusui Ingaritsu - Hanabi 2 (Japan) | PSX |
| Ooedo Senryoubako (Japan) | PSP |
| Ooga Booga (USA) | DC |
| Oogami Ichirou Funtouki - Sakura Taisen Kayou Show 'Kurenai Sekieki' Yori (Japan) | DC |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.0 B) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.0 D) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.0 K) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.0, set 1) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.0, set 2) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.1 B) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.1 D) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.1 K) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU4) (DR_ 2.1) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU5) (set 1) | MAME |
| Ooh Aah Dracula (Barcrest) (MPU5) (set 2) | MAME |
| Ooh Aah Dracula Club (Barcrest) (MPU5) (set 1) | MAME |
| Ooh Aah Dracula Club (Barcrest) (MPU5) (set 2) | MAME |
| Ooh Aah Dracula Club (Barcrest) (MPU5) (set 3) | MAME |
| Ooh Ahh Dracula Rio (Barcrest) (MPU5) | MAME |
| Ookami Kakushi (Japan) | PSP |
| Ookami to Koushinryou - Boku to Holo no Ichinen (J)(Navarac) | NDS |
| Ookami to Koushinryou - Umi wo Wataru Kaze (JP)(Tashiro) | NDS |
| Ookiku Furikabutte - Honto no Ace ni Nareru kamo (J)(6rz) | NDS |
| Oomono Black Bass Fishing - Jinzouko Hen (Japan) | SNES |
| Oonita Atsushi FMW - Kagekara no Chousen (Japan) | SNES |
| Oonita Atsushi FMW - Kagekara no Chousen (Japan) (Beta) | SNES |
| Oops (1988)(The Big Apple Entertainment Company) | ZX Spectrum Z80 |
| Ooze (1988)(Dragonware Games)(de)[cr Bladerunners][m EMT] | Atari ST |
| Ooze - Creepy Nites | Amiga |
| Ooze v1.2E (1988)(Dragonware Games) | Atari ST |
| Ooze v1.2E (1988)(Dragonware Games)[a] | Atari ST |
| Ooze, The (Europe) | Genesis |
| Ooze, The (Japan, USA) | Genesis |
| Oozumou - The Grand Sumo (DECO Cassette) (Japan) | MAME |
| Oozumou Damashii (Japan) | SNES |
| Opa Opa (Japan) | SMS |
| Opa Opa (MC-8123, 317-0042) | MAME |
| Open Door, The (1988)(Tartan Software) | ZX Spectrum Z80 |
| Open Door, The (1988)(Tartan Software) | ZX Spectrum (TAP) |
| Open Mahjong [BET] (Japan) | MAME |
| Open Quest (FanMade - Get's Detected as DOTT) | ScummVM |
| Open Season | GCN |
| Open Season (E)(Rising Sun) | GBA |
| Open Season (E)(Sir VG) | GBA |
| Open Season (E)(Supremacy) | NDS |
| Open Season (E)(Wet 'N' Wild) | NDS |
| Open Season (Europe) | PSP |
| Open Season (Europe) | PSP |
| Open Season (Europe) (En,Fr,De,Es,It) | GCN |
| Open Season (Europe) (En,Fr,De,Es,It,Nl,Sv,No,Da,Fi) | PS2 |
| Open Season (Europe) (En,Fr,Es) | GCN |
| Open Season (Europe) (En,Fr,Es,Nl) | PS2 |
| Open Season (U)(Legacy) | NDS |
| Open Season (U)(Rising Sun) | GBA |
| Open Season (USA) | PS2 |
| Open Season (USA) | PSP |
| Open Sesame (0351309, US) | MAME |
| Open Sesame (Bellfruit) (Scorpion 4) (set 1) | MAME |
| Open Sesame (Bellfruit) (Scorpion 4) (set 2) | MAME |
| Open The Box (Ace) (sp.ACE) (set 1) | MAME |
| Open The Box (Ace) (sp.ACE) (set 10) | MAME |
| Open The Box (Ace) (sp.ACE) (set 2) | MAME |
| Open The Box (Ace) (sp.ACE) (set 3) | MAME |
| Open The Box (Ace) (sp.ACE) (set 4) | MAME |
| Open The Box (Ace) (sp.ACE) (set 5) | MAME |
| Open The Box (Ace) (sp.ACE) (set 6) | MAME |
| Open The Box (Ace) (sp.ACE) (set 7) | MAME |
| Open The Box (Ace) (sp.ACE) (set 8) | MAME |
| Open The Box (Ace) (sp.ACE) (set 9) | MAME |
| Open The Box (Barcrest) (MPU5) (set 1) | MAME |
| Open The Box (Barcrest) (MPU5) (set 2) | MAME |
| Open The Box (Barcrest) (MPU5) (set 3) | MAME |
| Open The Box (Barcrest) (MPU5) (set 4) | MAME |
| Open, Sesame! - Sesam, Oeffne Dich (1982) (Bit Corporation) (PG204) (PAL) | 2600 |
| Opera Imaginaire (CD-i) | CD-I |
| Opera_House_Qa! | Atari 800 |
| Operacja Pustynna Burza | Atari 800 |
| Operation - Cleanstreets | Amiga |
| Operation - Frog (UE) | C64 PP |
| Operation - Vietnam (E)(EXiMiUS) | NDS |
| Operation - Vietnam (G)(EXiMiUS) | NDS |
| Operation - Vietnam (U)(XenoPhobia) | NDS |
| Operation Air Assault (Europe) | PS2 |
| Operation Air Assault 2 (Europe) | PS2 |
| Operation Apocalypse (1981)(SSI) | Apple2 |
