| One Piece - Gear Spirit (Korea) | |
| One Piece - Gigant Battle! (Europe) | |
| One Piece - Gigant Battle! (France) | |
| One Piece - Gigant Battle! (Germany) | |
| One Piece - Gigant Battle! (Japan) | |
| One Piece Gigant Battle 2 - Shin Sekai (Japan) | |
| Onegai My Melody - Yume no Kuni no Daibouken (Japan) | |
| Oni Zero - Sengoku Ranse Hyakka Ryouran (Japan) | |
| Onsei Kanjou Sokuteiki - Kokoro Scan (Japan) | |
| Ontama - Onpu-tou Hen (Japan) | |
| Ontamarama (USA) | |
| Ookami Den - Chiisaki Taiyou (Japan) | |
| Ookami Den (Europe) | |
| Ookami Den (USA) | |
| Ookami to Koushinryou - Boku to Holo no Ichinen (Japan) | |
| Ookami to Koushinryou - Umi o Wataru Kaze (Japan) | |
| Ookiku Furikabutte - Honto no Ace ni Nareru kamo (Japan) | |
| Open Season (Europe) (En,Es,It,Nl) | |
| Open Season (Europe) (En,Fr,De,Es,It,Sv,No,Da,Fi) | |
| Open Season (USA) (En,Fr,Es,Nl) | |
| Operation - Vietnam (Europe) (En,Fr,Es,It) | |
| Operation - Vietnam (Germany) | |
| Operation - Vietnam (USA) | |
| Orcs & Elves (Europe) (En,Fr,De,Es,It) | |
| Orcs & Elves (USA) (En,Fr,De,Es,It) | |
| Ore ga Omae o Mamoru (Japan) | |
| Ore no Sentouki (Japan) | |
| Original Frisbee Disc Sports - Ultimate & Golf (Europe) (En,Fr,De,Es,It) | |
| Original Frisbee Disc Sports - Ultimate & Golf (USA) | |
| Original Rummikub, The - Brings People Together (Europe) (En,Fr,De,Es,It,Nl) (DTP Entertainment AG) | |
| Original Rummikub, The - Brings People Together (Europe) (En,Fr,De,Es,It,Nl) (Games Factory Online) | |
| Osawari Tantei - Ozawa Rina - Season 2 1-2 - Rina wa Mita! Iya, Mite nai. (Japan) | |
| Osawari Tantei - Ozawa Rina (Japan) | |
| Oscar der Ballonfahrer - Tierische Abenteuer (Europe) (En,De) | |
| Oshaberi Oumu (Japan) | |
| Oshare Majo Love and Berry - DS Collection (Japan) | |
| Oshare na Koinu DS (Japan) | |
| Oshare Princess - Oshare ni Koishite (Japan) | |
| Oshare Princess - Oshare ni Koishite 2 (Japan) | |
| Oshiri Kajiri Mushi no Rhythm Lesson DS - Kawai Ongaku Kyoushitsu Kanshuu (Japan) | |
| Osu! Tatakae! Ouendan (Japan) | |
| Othello de Othello DS (Japan) | |
| Oto o Tsunagou! Gunpey-Rebirth (Japan) | |
| Otogi Juushi Akazukin (Japan) | |
| Otome-teki Koi Kakumei - Love Revo!! DS (Japan) | |
| Otona no DS Golf (Japan) | |
| Otona no DS Mystery - Izumi Jiken File (Japan) | |
| Otona no Onna Ryoku Kentei (Japan) | |
| Otona no Renai Shousetsu - DS Harlequin Selection (Japan) | |
| Otona Ryoku Kentei (Japan) | |