- Obliteracers (Xbox One)
- Observation (Xbox One)
- observer (Xbox One)
- Observer: System Redux (Xbox Series X|S)
- Oceanhorn: Monster of Uncharted Seas (Xbox One)
- Octodad: Dadliest Catch (Xbox One)
- Octonaut (Xbox One)
- Octopath Traveler (Xbox One)
- Odallus: The Dark Call (Xbox One)
- Oddworld Munch's Oddysee (Xbox)
- Oddworld Stranger's Wrath (Xbox)
- Oddworld: Abe’s Exoddus (Xbox One)
- Oddworld: New 'n' Tasty! (Xbox One)
- Odium to the Core (Xbox One)
- Of Tanks and Demons III (Xbox One)
- Offroad Racing - Buggy X ATV X Moto (Xbox One)
- Offworld Trading Company (Xbox for PC)
- Oh...Sir The Insult Simulator (Xbox One)
- Okami HD (Xbox One)
- Old Man's Journey (Xbox One)
- Oliver's Adventures in the Fairyland (Xbox One)
- OlliOlli (Xbox One)
- OlliOlli World (Xbox Series X|S)
- OlliOlli2: XL Edition (Xbox One)
- Olympic Games Tokyo 2020 - The Official Video Game (Xbox One)
- Omensight (Xbox One)
- Omori (Xbox Series X|S)
- On A Roll (Xbox 360)
- On A Roll (Xbox One)
- On Rusty Trails (Xbox One)
- One Dog Story (Xbox One)
- One Escape (Xbox Series X|S)
- One Finger Death Punch 2 (Xbox One)
- One Leaves (Xbox One)
- One Night Stand: Console Edition (Xbox One)
- One Piece Odyssey (Xbox Series X|S)
- One Piece Pirate Warriors 4 (Xbox One)
- ONE PIECE World Seeker (Xbox One)
- One Piece: Burning Blood (Xbox One)
- One Punch Man: A Hero Nobody Knows (Xbox One)
- Onigiri (Xbox One)
- Oniken (Xbox One)
- Onimusha: Warlords (Xbox One)
- Ooblets (Xbox One)
- Operencia: The Stolen Sun (Xbox One)
- Opus Magnum (Xbox for PC)
- OPUS: Echo of Starsong - Full Bloom Edition (Xbox Series X|S)
- ORBIT (Xbox One)
- Organic Panic (Xbox One)
- Ori And The Blind Forest (Xbox 360)
- Ori and the Blind Forest (Xbox One)
- Ori and the Blind Forest: Definitive Edition (Xbox One)
- Ori and the Will of the Wisps (Xbox Series X|S)
- Ori The Collection (Xbox Series X|S)
- Ostrich Island: Escape from Paradise (Xbox One)
- Othercide (Xbox One)
- Otogi 2: Immortal Warriors (Xbox)
- Outbreak (Xbox One)
- Outbreak: Epidemic (Xbox One)
- Outbreak: Lost Hope (Xbox One)
- Outbreak: Lost Hope Definitive Edition (Xbox Series X|S)
- Outbreak: The New Nightmare Definitive Edition (Xbox Series X|S)
- Outbreak: The Nightmare Chronicles Definitive Edition (Xbox Series X|S)
- Outbuddies DX (Xbox One)
- Outcast: Second Contact (Xbox One)
- Outer Wilds (Xbox One)
- Outland (Xbox 360)
- Outlast (Xbox One)
- Outlast 2 (Xbox One)
- Outriders (Xbox Series X|S)
- OutRun 2 (Xbox)
- Outward (Xbox One)
- Overcooked (Xbox One)
- Overcooked 2 (Xbox One)
- Overcooked! All You Can Eat (Xbox Series X|S)
- Overkill's The Walking Dead (Xbox One)
- Overland by Finji (Xbox One)
- Overload (Xbox One)
- Overlord: Fellowship of Evil (Xbox One)
- Overpass (Xbox One)
- Override 2: Super Mech League (Xbox Series X|S)
- Override: Mech City Brawl (Xbox One)
- Overruled! (Xbox One)
- Overwatch (Xbox One)
- Overwatch 2 (Xbox Series X|S)
- Overwatch: Origins Edition (Xbox One)
- Overwhelm (Xbox for PC)
- Ovivo (Xbox One)
- Owlboy (Xbox One)
- Oxenfree (Xbox One)