The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- O-Games (Publisher) (2 members)
- OG International (Publisher) (1 member)
- O Games (Publisher) (1 member)
- Obsidian Entertainment (Developer) (4 members)
- Obut Pétanque (Series) (2 members)
- Oddworld (Series) (3 members)
- Oddworld Inhabitants (Publisher) (3 members)
- Old School Games (Developer) (2 members)
- Omega Force (Developer) (33 members)
- Omni Systems (Developer) (1 member)
- One Piece (Series) (4 members)
- One True Game Studios (Developer) (1 member)
- Ongakukan (Developer) (2 members)
- Ongakukan (Publisher) (2 members)
- Operation Flashpoint (Series) (2 members)
- Orange Juice (Developer) (1 member)
- Other Ocean Interactive (Developer) (3 members)
- Output scaling: FidelityFX Super Resolution (FSR) (Config) (1 member)
- Over The Top Games (Developer) (1 member)
- Overkill Software (Developer) (2 members)
- PAN Vision (Publisher) (1 member)
- PGA Tour (Series) (8 members)
- PPU LLVM Java mode handling: False (Config) (0 members)
- PPU LLVM Java mode handling: True (Config) (0 members)
- PPU LLVM accurate vector NaNs: On (Config) (1 member)
- PPU decoder: Interpreter (static) (Config) (16 members)
- PPU thread count: 1 (Config) (1 member)
- PQube (Publisher) (7 members)
- PSN status: Disconnected (Config) (1 member)
- PSN status: RPCN (Config) (6 members)
- PSN status: Simulated (Config) (2 members)
- PSR Outdoors (Developer) (2 members)
- PSR Outdoors (Publisher) (2 members)
- Pac-Man (Series) (3 members)
- PachiPara (Series) (3 members)
- Pachinko (Genre) (14 members)
- Page 44 Studios (Developer) (1 member)
- Pages using duplicate arguments in template calls (15 members)
- Pages using vgregion with named parameters (1 member)
- Pages with broken file links (1 member)
- Pages with too many expensive parser function calls (0 members)
- Pandemic Studios (Developer) (3 members)
- Paon Corporation (Developer) (1 member)
- Paon Corporation (Publisher) (1 member)
- Papaya Studio (Developer) (2 members)
- Paradigm Entertainment (Developer) (1 member)
- Paradox Interactive (Publisher) (2 members)
- Paramount Digital Entertainment (Publisher) (4 members)
- Party (Genre) (24 members)
- Patches available (273 members)