| Game Name | System |
|---|
| Optix 2 by Benediction (F) (2001) (PD) | CPC |
| Opus No.1 (19xx)(Bach, Christian)(FW) | Atari ST |
| Ora Ora Ball (1995)(Ora Soft)(Disk 1 of 2) | X68K |
| Ora Ora Ball (1995)(Ora Soft)(Disk 2 of 2) | X68K |
| Ora-Shoot (1996)(Ora Soft)(Disk 1 of 2) | X68K |
| Ora-Shoot (1996)(Ora Soft)(Disk 2 of 2) | X68K |
| Ora-Shoot (1996)(Ora Soft)(Disk 2 of 2)[a] | X68K |
| Oracle (Dutch) (Bellfruit) (Scorpion 1) | MAME |
| Oracle no Houseki - Jewels of the Oracle (Japan) (En,Ja,Fr,De) | PSX |
| Oracle's Cave, The (1984)(Doric Computer Services) | ZX Spectrum Z80 |
| Oracle's Cave, The (1984)(Doric Computer Services) | ZX Spectrum (TAP) |
| Oracle's Cave, The (1984)(Doric Computer Services)[a] | ZX Spectrum Z80 |
| Oraga Land Shusai - Best Farmer Shuukakusai (Japan) | SNES |
| Oraga Land Shusai - Best Farmer Shuukakusai (Japan) (Sample) | SNES |
| Orange Club - Maru-hi Ippatsu Kaihou [BET] (Japan 880221) | MAME |
| Orange Club - Maruhi Kagai Jugyou (Japan 880213) | MAME |
| Orange Iro No Biyaku (1989)(System House Oh!) | X68K |
| Oranges & Lemons (1983)(K.J.B.) | Atari 800 |
| Orao 102 | MAME |
| Orao 103 | MAME |
| Orb | Atari 800 |
| Orb 3D (USA) | NES |
| Orb of Zarramier | Atari 800 |
| Orb pinball | Atari 800 |
| Orb, L' (19xx)(Budgie UK)(LW) | Atari ST |
| Orbatak (prototype) | MAME |
| Orbis Pictus - Anglictina | Atari 800 |
| Orbis Pictus - Nemcina | Atari 800 |
| Orbit | MAME |
| Orbit (1996)(CSSCGC) | ZX Spectrum Z80 |
| Orbit (19xx)(-)(ST) | Atari ST |
| Orbit (19xx)(R. S. Horne)[k-file] | Atari 800 |
| Orbit - A Trip to the Moon | Atari 800 |
| Orbit 1 | MAME |
| Orbital (1989)(Impact)[a2][bootfile] [SSD] | BBC Micro |
| Orbital (1989)(Impact)[a][bootfile] [SSD] | BBC Micro |
| Orbital (1989)(Impact)[bootfile] [SSD] | BBC Micro |
| Orbital (1989)(Impact)[h TSTH][bootfile] [SSD] | BBC Micro |
| Orbital_Simulation | Atari 800 |
| Orbiter (1982)(Silversoft) | ZX Spectrum Z80 |
| Orbiter (1982)(Silversoft) | ZX Spectrum (TAP) |
| Orbiter (1982)(Silversoft)[a] | ZX Spectrum Z80 |
| Orbiter (1988)(Spectrum Holobyte)(Disk 1 of x)[cr Arcadian][b] | Atari ST |
| Orbiter v1.01 (1988)(Spectrum Holobyte)(Disk 1 of 2) | Atari ST |
| Orbiter v1.01 (1988)(Spectrum Holobyte)(Disk 1 of 2)[a] | Atari ST |
| Orbiter v1.01 (1988)(Spectrum Holobyte)(Disk 2 of 2) | Atari ST |
| Orbiter v1.01 (1988)(Spectrum Holobyte)(Disk 2 of 2)[a] | Atari ST |
| Orbitor 1 | MAME |
| Orbitron | MAME |
| Orbitron (E) | C64 Tapes |
| Orbits (1992)(Winter Tech)(F) | DOS |
| Orbix The Terrorball (1986)(Domark) | ZX Spectrum Z80 |
| Orbix The Terrorball (1986)(Domark) | ZX Spectrum (TAP) |
| Orbix The Terrorball (1986)(Domark)[a] | ZX Spectrum Z80 |
| Orbs (10/7/94 prototype?) | MAME |
| Orc Attack (1983)(T.E.V.)[k-file] | Atari 800 |
| Orc Attack (1984)(Creative Sparks) | ZX Spectrum (TAP) |
| Orc Attack (1984)(Creative Sparks) | ZX Spectrum Z80 |
| Orc Attack (1984)(Creative Sparks)[a] | ZX Spectrum Z80 |
| Orc Attack (E) | C64 Tapes |
| Orc Attack (E) [alt] | C64 Tapes |
| Orc Island (19xx)(Double Play Adventures) | ZX Spectrum Z80 |
| Orc Island (19xx)(Double Play Adventures)[a] | ZX Spectrum Z80 |
| OrcAttack | Atari 800 |
| Orchid Mist (0100849V, NSW/ACT) | MAME |
| Orchid Mist (0200849V, NSW/ACT) | MAME |
| Orcrest (19xx)(-)[bootfile] [SSD] | BBC Micro |
| Orcrest (19xx)(-)[h TSTH][t +2][bootfile-invulnerability-Master] [SSD] | BBC Micro |
| Orcs & Elves (E)(sUppLeX) | NDS |
| Orcs & Elves (U)(XenoPhobia) | NDS |
| Order of the Griffon (USA) | TG16 |
| Ordisavant (France) | MAME |
| Ordralphabetix | Atari 800 |
| Ordyne (Japan) | MAME |
| Ordyne (Japan) | TG16 |
| Ordyne (Japan, English Version) | MAME |
| Ordyne (USA) | TG16 |
| Ore No Ryouri (Japan) | PSX |
| Ore ga Omae o Mamoru (JP)(Caravan) | NDS |
| Ore no Dungeon - Desire and Adventurous Spirit (Japan) | PSP |
| Ore no Imouto Maker EX Portable (Japan) | PSP |
| Ore no Imouto ga Konna ni Kawaii Wake ga Nai - Portable ga Tsuzuku Wake ga Nai (UMD Disc 1) (Japan) | PSP |
| Ore no Imouto ga Konna ni Kawaii wake ga Nai Portable (Japan) | PSP |
| Ore no Sentoki (J)(SCZ) | NDS |
| Ore no Shikabane o Koete Yuke (Japan) | PSP |
| Ore no Shikabane wo Koete Yuke (Japan) | PSX |
| Ore wa Shoujo Mangaka (Japan) | PSP |
| Ore! Tomba (Japan) | PSX |
| Oregon Trail (1990)(Mecc) | DOS |
| Oregon_Trail | Atari 800 |
| Oretachi Geasen Zoku Sono - Nekketsu Kouha Kunio-kun (Japan) | PS2 |
| Oretachi no Sabage Portable (Japan) | PSP |
| Oretachi no Sabage Versus (Japan) | PSP |
| Organ (19xx)(-) | ZX Spectrum Z80 |
| Organiser I | MAME |
| Organiser II CM | MAME |
| Organiser II LA | MAME |
| Organiser II LAM | MAME |
| Organiser II LZ | MAME |
| Organiser II LZ64 | MAME |
