| Game Name | System |
|---|
| Oriental Beauty (10213511, NSW/ACT) | MAME |
| Oriental Diamonds (Barcrest) (German) (MPU4) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 105, Korean Board) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 111, Chinese Board) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 111, Korean Board) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 111, Taiwanese Board) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 112) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 112, Chinese Board) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. 126) | MAME |
| Oriental Legend / Xi You Shi E Zhuan (ver. ???, Chinese Board) | MAME |
| Oriental Legend 2 (V101, China) | MAME |
| Oriental Legend 2 (V103, China) | MAME |
| Oriental Legend 2 (V104, China) | MAME |
| Oriental Legend Special / Xi You Shi E Zhuan Super (ver. 100, set 1) | MAME |
| Oriental Legend Special / Xi You Shi E Zhuan Super (ver. 100, set 2) | MAME |
| Oriental Legend Special / Xi You Shi E Zhuan Super (ver. 101, Korean Board) | MAME |
| Oriental Legend Special / Xi You Shi E Zhuan Super (ver. 103, China, Tencent) (unprotected) | MAME |
| Oriental Legend Special Plus / Xi You Shi E Zhuan Super Plus | MAME |
| Orion 128 | MAME |
| Orion 128 (MS7007) | MAME |
| Orion 128 + Z80 Card II | MAME |
| Orion 128 + Z80 Card II (MS7007) | MAME |
| Orion 128 + Z80 Card II + IDE | MAME |
| Orion 128 + Z80 Card II + IDE (MS7007) | MAME |
| Orion Pro | MAME |
| Orius (ver UAA) | MAME |
| Orizon-Micro | MAME |
| Orlando Magic (Bwb) (MPU4) (set 1) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 2) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 3) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 4) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 5) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 6) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 7) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 8) | MAME |
| Orlando Magic (Bwb) (MPU4) (set 9) | MAME |
| Osborne-1 | MAME |
| Osborne-1 (Nuevo Video) | MAME |
| Oscar (0100348V, NSW/ACT) | MAME |
| Oscar (0200348V, NSW/ACT) | MAME |
| Osman (World) | MAME |
| Otenami Haiken (V2.04J 1999/02/01 18:00:00) | MAME |
| Otenami Haiken Final (V2.07JC 2005/04/20 15:36) | MAME |
| Otenki Kororin (V2.01J 2001/07/02 10:00) | MAME |
| Othello (version 3.0) | MAME |
| Othello Derby (Japan) | MAME |
| Othello Multivision FG-1000 | MAME |
| Othello Multivision FG-2000 | MAME |
| Othello Shiyouyo (J 980423 V1.002) | MAME |
| Otogizoushi Urashima Mahjong (Japan) | MAME |
| Otona no Mahjong (Japan 880628) | MAME |
| Ougon no Shiro (Japan) | MAME |
| Out Run (Japan, deluxe sitdown) (FD1089A 317-0019) | MAME |
| Out Run (Mega-Tech, SMS based) | MAME |
| Out Run (bootleg) | MAME |
| Out Run (deluxe sitdown earlier version) | MAME |
| Out Run (deluxe sitdown) | MAME |
| Out Run (deluxe sitdown) (Enhanced Edition v1.0.3) | MAME |
| Out Run (sitdown/upright, Rev A) | MAME |
| Out Run (sitdown/upright, Rev B) | MAME |
| Out Run (sitdown/upright, Rev B) (Enhanced Edition v1.1.0) | MAME |
| Out Zone | MAME |
| Out Zone (Zero Wing TP-015 PCB conversion) | MAME |
| Out Zone (harder) | MAME |
| Out Zone (old set) | MAME |
| Out Zone (older set) | MAME |
| Out Zone (oldest set) | MAME |
| OutRun 2 (Rev A) (GDX-0004A) | MAME |
| OutRun 2 SP SDX | MAME |
| OutRun 2 Special Tours (GDX-0014) | MAME |
| OutRun 2 Special Tours (Japan) (Rev A) (GDX-0011A) | MAME |
| OutRun 2 Special Tours (Rev A) (GDX-0014A) | MAME |
| OutRunners (Japan) | MAME |
| OutRunners (US) | MAME |
| OutRunners (World) | MAME |
| OutTrigger | MAME |
| Outback Jack (20195211, NSW/ACT) | MAME |
| Outlaw (Bellfruit) (Scorpion 4) (set 1) | MAME |
| Outlaw (Bellfruit) (Scorpion 4) (set 2) | MAME |
| Outlaw (Bellfruit) (Scorpion 4) (set 3) | MAME |
| Outlaw (Bellfruit) (Scorpion 4) (set 4) | MAME |
| Outlaw (JPM) (IMPACT, Club?) | MAME |
| Outlaw (JPM) (IMPACT, v3) | MAME |
| Outlaw (JPM) (IMPACT, v3) (Protocol) | MAME |
| Outlaw [TTL] | MAME |
| Outline | MAME |
| Over Drive (set 1) | MAME |
| Over Drive (set 2) | MAME |
| Over Drive (set 3) | MAME |
| Over Moon Pt3 (Bwb) (MPU4 Video) | MAME |
| Over Rev (Model 2B, Revision B) | MAME |
| Over Rev (Model 2C, Revision A) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1 B) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1 C) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1 K) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1 KD) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1 Y) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1 YD) | MAME |
| Over The Moon (Barcrest) (MPU4) (OT8 0.1) | MAME |
| Over The Moon (Barcrest) (MPU4) (OTN 0.5 B) | MAME |
