- O.R.B.: Off-World Resource Base
- Obduction
- Obliteracers
- ObsCure
- ObsCure II
- Observation
- Observer
- Occupy White Walls
- Oceanhorn
- Octahedron
- Octodad
- Octodad: Dadliest Catch
- Octogeddon
- Octomania
- Octopath Traveler
- Odallus: The Dark Call
- Oddmar
- Oddworld: Abe's Exoddus
- Oddworld: Abe's Oddysee
- Oddworld: Munch's Oddysee
- Oddworld: Soulstorm
- Oddworld: Soulstorm - Enhanced Edition
- Oddworld: Stranger's Wrath
- Ode
- Odin Sphere
- Odium To the Core
- Odysseus Kosmos and his Robot Quest
- Of Guards And Thieves
- Of Orcs and Men
- OFF
- Off-Peak
- Office Freakout
- Offroad Outlaws
- Offspring Fling!
- Offworld Trading Company
- OGame
- Ogre Battle 64: Person of Lordly Caliber
- Ogre Battle: The March of the Black Queen
- Oh My Godheads
- Oh No! More Lemmings
- Oh...Sir! The Hollywood Roast
- Oh...Sir!! The Insult Simulator
- Oil Rush
- OK K.O.! Let's Play Heroes
- OK/NORMAL
- Okabu
- Ōkami
- Ōkamiden
- Okhlos: Omega
- Oknytt
- OkunoKa Madness
- Old Man's Journey
- Old School Musical
- Old School RuneScape
- Old World
- Olija
- OlliOlli
- OlliOlli World
- OlliOlli2: Welcome to Olliwood
- Omega Boost
- Omega Five
- Omega Quintet
- Omega Strike
- Omensight
- Omensight: Definitive Edition
- Omerta: City of Gangsters
- OMG Zombies!
- Omikron: The Nomad Soul
- Omnibus
- OMNO
- Omori
- On My Own
- On Rusty Trails
- Once Chance
- One Dog Story
- One Eyed Kutkh
- One Finger Death Punch
- One Finger Death Punch 2
- One More Dungeon
- One More Line
- One Must Fall: 2097
- One Night Stand
- one night, hot springs
- One Piece - Gigant Battle!
- One Piece: Burning Blood
- One Piece: Gigant Battle!
- One Piece: Grand Adventure
- One Piece: Grand Battle!
- One Piece: Grand Battle! Rush
- One Piece: Pirate Warriors
- One Piece: Pirate Warriors 2
- One Piece: Pirate Warriors 3
- One Piece: Pirate Warriors 3 - Deluxe Edition
- One Piece: Pirate Warriors 4
- One Piece: Pirates' Carnival
- One Piece: Romance Dawn
- One Piece: Treasure Cruise
- One Piece: Unlimited Adventure
- One Piece: Unlimited Cruise SP
- One Piece: Unlimited World RED
- One Piece: World Seeker
- One Punch Man: A Hero Nobody Knows
- One Step From Eden
- One Strike
- One Thousand Lies
- One Troll Army
- One Upon Light
- One Way Heroics
- One Way Trip
- Onechanbara Z2: Chaos
- Onechanbara: Bikini Samurai Squad
- OneChanbara: Bikini Zombie Slayers
- OneShot
- Oni
- Onigiri
- Oniken
- Onimusha 2: Samurai's Destiny
- Onimusha 3: Demon Siege
- Onimusha Tactics
- Onimusha: Blade Warriors
- Onimusha: Dawn of Dreams
- Onimusha: Warlords
- Oninaki
- Onirim - Solitaire Card Game
- Only If
- Onmyoji
- ONRUSH
- Onward
- Ooblets
- Oozi: Earth Adventure
- Open Country
- Open Season
- OpenTTD
- Operation Abyss: New Tokyo Legacy
- Operation Babel: New Tokyo Legacy
- Operation C
- Operation Darkness
- Operation Flashpoint: Cold War Crisis
- Operation Flashpoint: Dragon Rising
- Operation Flashpoint: Elite
- Operation Flashpoint: Red River
- Operation Thunderstorm
- Operation Wolf
- Operation: Matriarchy
- Operation: Tango
- Operation: Vietnam
- Operencia: The Stolen Sun
- Opoona
- Oppai Slider 2
- Opus Magnum
- OPUS: Rocket of Whispers
- OPUS: The Day We Found Earth
- Orbital Gear
- orbt xl
- Orcs & Elves
- Orcs Must Die!
- Orcs Must Die! 2
- Orcs Must Die! 3
- Orcs Must Die! Unchained
- Order of Battle: World War II
- Order of War
- Order Up!
- Oreshika: Tainted Bloodlines
- Organ Trail
- Organ Trail: Director's Cut
- Ori and the Blind Forest
- Ori and the Will of the Wisps
- Oriental Empires
- Original Journey
- Original War
- ORION: Prelude
- Orwell
- Orwell: Ignorance is Strength
- Oscura: Lost Light
- Osiris: New Dawn
- Osmos
- Ostriv
- osu!
- Osu! Tatakae! Ouendan
- Otaku's Adventure
- Othello
- Othercide
- Otogi: Myth of Demons
- Otomedius Excellent
- Our World is Ended
- Out of Ammo
- Out of Line
- Out of the Park Baseball 16
- Out of the Park Baseball 17
- Out of the Park Baseball 18
- Out of the Park Baseball 19
- Out of the Park Baseball 20
- Out There
- Out There Somewhere
- Out There: Ω Edition
- Outcast
- Outcry
- OutDrive
- Outer Wilds
- Outland
- Outlast
- Outlast II
- Outlaw
- Outlaw Tennis
- Outlaw Volleyball
- Outlaws
- Outpost Kaloki X
- Outriders
- OutRun
- OutRun 2
- OutRun 2006: Coast 2 Coast
- Outrun Online Arcade
- Outward
- Outward: Definitive Edition
- Over 9000 Zombies!
- Over G Fighters
- Over The Hedge
- Over the Hedge: Hammy Goes Nuts!
- Overboard!
- Overclocked: A History of Violence
- Overcooked!
- Overcooked! 2
- Overcrowd: A Commute 'Em Up
- Overfall
- Overgrowth
- OVERKILL's The Walking Dead
- Overland
- Overload
- Overlord
- Overlord II
- Overlord: Dark Legend
- Overlord: Fellowship of Evil
- Overpower
- Override 2: Super Mech League
- Override: Mech City Brawl
- Overruled
- Overwatch
- Overwatch: Game of the Year Edition
- Overwhelm
- OVIVO
- Owlboy
- Oxenfree
- Oxygen Not Included
- OZMAFIA!!