| Overboundn | Developer | |
| Overflow | Developer | |
| Overgame Studio | DeveloperPublisher | |
| Overgrown | Developer | |
| Overhead Games | Developer | |
| Overkill Software | Developer | |
| Overmax Studios | Developer | |
| Overpowered Games | Developer | |
| Overseas | Developer | |
| Overtired_FOX | Developer | |
| Overtold | Developer | |
| OverwaterGames Official | Developer | |
| OverworkedStudios | Developer | |
| Overworks | DeveloperPublisher | |
| Overworld Galaxy | Developer | |
| Ovid Works | Developer | |
| Ovidiu Barac | Developer | |
| Ovine by Design | DeveloperPublisher | |
| Ovosonico | Developer | |
| OwT | Developer | |
| Owen Ayers | Developer | |
| Owen Brunette | Developer | |
| Owen Deery | Developer | |
| Owen Emry | Developer | |
| Owen Heinz | Developer | |
| OwenM45 | Developer | |
| OwenSenior | Developer | |
| OwenTheBell | Developer | |
| Owhno | Developer | |
| Owl Nest Studios | Developer | |
| Owl Sanctuary Studios | Developer | |
| OwlTechInteractive | Developer | |
| OwllCraft | Developer | |
| Owlor | Developer | |
| OwlyCode | Developer | |
| Owned by Gravity | Developer | |
| Ox Flame Game Dev | Developer | |
| Oxbane Project | Developer | |
| Oxeye Game Studio | DeveloperPublisher | |
| Oxford Digital Enterprises | Developer | |
| Oxford Digital Enterprises (Kevin R. Ayre) | Developer | |
| Oxford Digital Enterprises (Michael Fox) | Developer | |
| Oxford Digital Enterprises Ltd. | Developer | |
| Oxford Mobius | Developer | |
| Oxford Softworks | DeveloperPublisher | |
| OxfordLucrezia | Developer | |
| OxiWan | Developer | |
| Oxidental Games | Developer | |
| Oxonian Games | Developer | |
| Oxygen Games | DeveloperPublisher | |
| Oxygen GamesEU | Publisher | |
| Oxygen GamesPAL | Publisher | |
| Oxygen Interactive | DeveloperPublisher | |
| Oxygen Studios | Developer | |
| Oxygene Media | DeveloperPublisher | |
| Oyadi | Developer | |
| Oyedoyin | Developer | |
| Oyuncu112 | Developer | |
| Oz Club | DeveloperPublisher | |
| Oz Software | Developer | |
| Ozark Softscape | Developer | |
| Ozark Software | Developer | |
| Ozdeger | Developer | |
| OziSoft AU | Publisher | |
| Ozla Pictures | Developer | |
| O~3 Entertainment | Publisher | |
| O~3 EntertainmentNA | Publisher | |
| P Jackson | Developer | |
| P Knecht | Developer | |
| P&P Marketing | Publisher | |
| P-PAMda | Developer | |
| P-Squared Productions | Developer | |
| P-Studio | Developer | |
| P. Sudon | Developer | |
| P.I.S.C. | Developer | |
| P.J. Soft | DeveloperPublisher | |
| P.J. Software (Carlos Coronel) | Developer | |
| P.J. Software (Josoft, Carlos Coronel) | Developer | |
| P.K. McManus | Developer | |
| P.Rahjoe | Developer | |
| P.S. ASSA | Developer | |
| P.S.S. | Publisher | |
| P.Z.Karen Co. | Developer | |
| P.Z.Karen Co. Development Group | Developer | |
| P0lter | Developer | |
| P1X | Developer | |
| P1xelFang | Developer | |
| P2 Games | DeveloperPublisher | |
| P2P Pte. Ltd. | Publisher | |
| P32nicky | Developer | |
| P4thog3n | Developer | |
| PAL | Publisher | |
| PAL Developments | Developer | |
| PAL Developments (Dave Thompson) | Developer | |
| PAL Developments (Dave Thompson, Richard Morton) | Developer | |
| PAL Developments (David Spicer, Jason Brashill) | Developer | |
| PAL Developments (Kevin Nichol, Chris Moorehouse) | Developer | |
| PAL Developments (Mark Wallace, Richard Morton, Sean Conran) | Developer | |
| PAL Developments (Mongee Boswell) | Developer | |
| PAL Developments (Richard Stevenson) | Developer | |