| opps3 | Darksiders Game Package |
| ork | Warhammer: Mark of Chaos Game Archive |
| orz | Holic Online Game Data |
| osb | Osu! Beatmap Script |
| osf | Descent 3 Outrage Sound |
| osk | Osu! Skin File |
| osn | OMSI Saved Situation |
| osr | Osu! Replay File |
| osu | Osu! Script |
| otd | OpenIV Texture Data |
| otfont | OpenTibia Font Data |
| otml | OpenTibia OTML Data |
| otmod | OpenTibia Mod Data |
| otps | OpenTibia Data |
| otr | Over the Reich Saved Game |
| otui | OpenTibia User Interface Data |
| ovh | OMSI Vehicle Configuration File |
| ovk | Little Busters Game Data |
| ovl | Rollercoaster Tycoon 3 Data |
| owp | Original War Game Package |
| ozb | MU Online Image |
| ozj | MU Online Image |
| ozt | MU Online Image |
| paa | Armed Assault Texture Data |
| packed | Jericho Game Data |
| packmeta | Quantum Break Package Metadata |
| pak | Quake Engine Data |
| paz | Black Desert Game Data |
| pb2map | Plazma Burst 2 Custom Map |
| pbo | Operation Flashpoint Data |
| pck | Perfect World Package |
| pcpack | Spider-Man 3 PC Game Data |
| pcsav | Mass Effect 2 Saved Game |
| pcsxstate | PCSX Saved State |
| pdlc | Farming Simulator Downloadable Content Package |