| O.J. Kart - Bronco Dash | WORLD | |
| Prototype |
| Obake no Q Tarou - Wanwan Panic | JP | 1985-12 |
Bandai | Commercial |
| Obocchama-kun | JP | 1991-04-05 |
Tecmo | Commercial |
| Obstacle Trek | WORLD | |
| Prototype |
| Obuchayushchiy Kartridzh | RU | |
| Unlicensed |
| Octops Octops | WORLD | 2025-04 |
James Tall | Unlicensed |
| Odyssey 1157 | WORLD | |
| Prototype |
| Oeka Kids - Anpanman no Hiragana Daisuki | JP | 1991-03-26 |
Bandai Namco | Commercial |
| Oeka Kids - Anpanman to Oekaki Shiyou!! | JP | 1990-10-25 |
Bandai Namco | Commercial |
| Oishinbo - Kyuukyoku no Menu Sanbon Shoubu | JP | 1989-07 |
Bandai | Commercial |
| Okkotoshi Puzzle - Tonjan! | JP | 1989-09-29 |
Jaleco | Commercial |
| Okkotoshi Puzzle - Tonjan! | JP | 1989-09-29 |
Jaleco | Prototype |
| Old Towers | WORLD | 2024-11 |
RetroSouls | Unlicensed |
| Old World | WORLD | |
| Prototype |
| Old World - Aftermath | WORLD | |
| Prototype |
| Old World - The Last Droid | WORLD | |
| Prototype |
| Oliver's Shell - An Adventure Story | WORLD | |
| Unlicensed |
| Olympic | AS | |
| Unlicensed |
| Olympic 2000 - 1000000-in-1 | AS | |
| Unlicensed |
| Olympic 2000 - 500-in-1 | TW | |
| Unlicensed |
| Olympic I.Q | KR | 1991 |
Sachen | Unlicensed |
| Olympic I.Q | TW | 1991 |
Sachen | Unlicensed |
| Olympus no Tatakai | JP | 1988-03 |
Brøderbund Software | Commercial |
| Omega Driver | WORLD | |
| Prototype |
| Once Upon a Time in China | WORLD | 2005 |
| Unlicensed |
| Oneshot | WORLD | |
| Prototype |
| Onyanko Town | JP | 1985-11-21 |
Pony Canyon | Commercial |
| Oof McBrewster's Haunted House Adventure | WORLD | 2020-11 |
Razzie.P | Unlicensed |
| Oopie's Quest | WORLD | |
| Unlicensed |
| Open Minded | WORLD | |
| Demo |
| Operation Secret Storm | US | 1991 |
Color Dreams | Unlicensed |
| Operation Wolf | EU | 1992 |
Taito | Commercial |
| Operation Wolf | JP | 1989-03-31 |
Taito | Commercial |
| Operation Wolf | US | 1989-05 |
Taito | Commercial |
| Oratorio | WORLD | 2022-09 |
John Vanderhoef | Demo |
| Orb-3D | US | 1990-10 |
HiTech Software | Commercial |
| Orebody - Binder's Tale | WORLD | 2022-12 |
Premium Edition Games | Demo |
| Orebody - Binder's Tale | WORLD | 2022-12 |
Premium Edition Games | Unlicensed |
| Orebody - Sand Ripples | WORLD | 2022-02 |
John Vanderhoef | Unlicensed |
| Os Cavaleiros do Zodiaco | AS | |
| Unlicensed |
| Osomatsu-kun - Back to the Me no Deppa no Maki | JP | 1989-12-08 |
Bandai | Commercial |
| Otaku no Seiza - An Adventure in the Otaku Galaxy | JP | 1991-07-31 |
M&M | Commercial |
| Othello | AU | 1986-11-13 |
Acclaim Entertainment | Unlicensed |
| Othello | JP | 1986-11-13 |
Acclaim Entertainment | Commercial |
| Othello | JP | 1986-11-13 |
Acclaim Entertainment | Prototype |
| Othello | TW | 1986-11-13 |
Kawada | Unlicensed |
| Othello | US | 1988-12 |
Acclaim Entertainment | Commercial |
| Oulu Zhi Zhan | CN | |
| Unlicensed |
| Ouroboros | WORLD | |
| Unlicensed |
| Outlanders | JP | 1987-12-04 |
Victor Entertainment | Commercial |
| Over Horizon | EU | 1992-09-13 |
Hot-B | Commercial |
| Over Horizon | JP | 1991-04-26 |
Hot-B | Commercial |
| Over Horizon - Fei Li Hangdao | AS | 1991-04 |
| Unlicensed |
| Overclocked | WORLD | |
| Unlicensed |
| Overlord | US | 1993-01 |
Virgin | Commercial |
| Overlord | US | 1993-01 |
Virgin Interactive | Prototype |