| Oedo Fight (Japan Bloodshed Ver.) | |
| Offensive (Spanish bootleg of Scramble) [Bootleg] | |
| Oh My God! | |
| Oishii Puzzle Ha Irimasenka | |
| Omega [Bootleg] | |
| Omega [Bootleg] | |
| Omega Fighter | |
| Omega Fighter Special | |
| Omni [Bootleg] | |
| One + Two | |
| One + Two (earlier) | |
| Oni - The Ninja Master (Japan) | |
| Onna Sansirou - Typhoon Gal (set 1) | |
| Onna Sansirou - Typhoon Gal (set 2) | |
| Operation Bear [Bootleg] | |
| Operation Thunderbolt (Japan, SC) | |
| Operation Thunderbolt (Japan) | |
| Operation Thunderbolt (US, older) | |
| Operation Thunderbolt (US) | |
| Operation Thunderbolt (World) | |
| Operation Wolf (Japan, SC) | |
| Operation Wolf (Japan) | |
| Operation Wolf (US) | |
| Operation Wolf (World, set 1) | |
| Operation Wolf (World, set 2) | |
| Operation Wolf 3 (US) | |
| Operation Wolf 3 (World) | |
| Orbitron | |
| Orbs (10/7/94 prototype?) | |
| Ordyne (Japan, English Version) | |
| Ordyne (Japan) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V111, China) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V111, Korea) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V111, Taiwan) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V112 alt, China) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V112, China) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V112) | |
| Oriental Legend - Xi Yo Gi Shi Re Zuang (V126) | |
| Oriental Legend (V105, Korea) | |
| Oriental Legend 2 (V104, Oversea) | |
| Oriental Legend Special - Xi Yo Gi Shi Re Zuang Super (V100) [Imperfect Protection Emulation] | |
| Oriental Legend Special - Xi Yo Gi Shi Re Zuang Super (V103, China, Tencent) (unprotected) | |
| Oriental Legend Special Plus / Xi You Shi E Zhuan Super Plus (ver. 205) [Incomplete Dump] | |
| Oriental Legend Super (V101, Korea) [Imperfect Protection Emulation] | |
| Orius (ver UAA) | |
| Osman (World) | |
| Out Run (bootleg) [Bootleg] | |
| Out Run (deluxe sitdown earlier version) | |
| Out Run (deluxe sitdown) | |
| Out Run (deluxe sitdown) (Enhanced Edition v1.0.3) | |