| Ochainu Kururin (J)(Caravan) | |
| Ochainu no Bouken Jima (J)(sUppLeX) | |
| Ochaken No Heya (J)(Rising Sun) | |
| Ochaken no Yumebouken (J)(Caravan) | |
| Oddworld - Munch's Oddysee (G)(Rising Sun) | |
| Oddworld - Munch's Oddysee (U)(Rising Sun) | |
| Ohanaya-san Monogatari (J)(GBANow) | |
| Ohanaya-san ni narou! (J)(kaMX) | |
| Ojaru Maru - Tsuki Hikari Machi Tour de Ojaru (J)(Trashman) | |
| Okaitoku Series 5 - Puzzle & Tantei Collection (J)(Patience) | |
| Okuman Chouja Game (J)(Independent) | |
| One Piece - Going Baseball Haejeok Yaku (K)(Independent) | |
| One Piece - Mezase! King of Paris (J)(Cezar) | |
| One Piece - Nanatsu Shima no Daihihou (J)(Cezar) | |
| One Piece Dragon Dream (J)(Caravan) | |
| One Piece Going Baseball (J)(Eurasia) | |
| Onimusha Tactics (E)(Patience) | |
| Onimusha Tactics (J)(Eurasia) | |
| Onimusha Tactics (U)(Mode7) | |
| Onmyou Taisenki Zeroshiki (J)(Caravan) | |
| Open Season (E)(Rising Sun) | |
| Open Season (E)(Sir VG) | |
| Open Season (U)(Rising Sun) | |
| Operation Armored Liberty (U)(Rising Sun) | |
| Oriental Blue - Ao no Tengai (J)(Cezar) | |
| Original Sunset Wilds title card & sprites for MK - SC by SCD | |
| Oshaberi Inco Club (J)(Chakky) | |
| Oshare Princess (J)(Chakky) | |
| Oshare Princess 2 And Doubutsu Kyaranabi (J)(Mugs) | |
| Oshare Princess 3 (J)(Rising Sun) | |
| Oshare Princess 5 (J)(Supplex) | |
| Oshare Princess EX Primo Debut Monogatari & Renai Uranai Daisakusen (J)(Caravan) | |
| Oshare Wanko (J)(Supplex) | |
| Ottifanten Pinball (G)(Rising Sun) | |
| Ougon no Taiyo (J)(Eurasia) | |
| Ougon no Taiyou - Shitsu Warate Jidai (J)(Eurasia) | |
| Our Breeding Series - My Ameba (J)(Eurasia) | |
| Our Breeding Series - My Beetle (J)(Eurasia) | |
| Over the Hedge - Beesten Bij de Buren (N)(Independent) | |
| Over the Hedge - Hammy Goes Nuts (E)(Rising Sun) | |
| Over the Hedge - Hammy Goes Nuts (U)(Rising Sun) | |
| Over the Hedge (E)(Independent) | |
| Over the Hedge (U)(Trashman) | |
| Ozzy & Drix (U)(Independent) | |