| un3 | Unreal 2: The Awakening Game Data |
| ung | Unigine Game Engine Data |
| unity | Unity 3D Scene |
| unity3d | Unity Web Player File |
| unitypackage | Unity Package File |
| unr | Unreal Level Map |
| updatr | iConomy Update |
| upk | Unreal Engine 3 Package |
| uqm | The Ur-Quan Masters Game Data |
| usa | Unreal Saved Game |
| usx | Unreal Tournament Static Meshes |
| ut2 | Unreal Tournament 2003 Map File |
| ut2mod | Unreal Tournament 2003 Module |
| ut3 | Unreal Tournament 3 Map |
| ut4mod | Unreal Tournament 2004 Module |
| ut8 | Ghost Master Language Data |
| utc | Bioware Aurora Creature Data |
| utd | Bioware Aurora Door Object |
| ute | Bioware Aurora Encounter Data |
| uti | Bioware Aurora Item Data |
| utm | Bioware Aurora Store Data |
| utp | Bioware Aurora Placeable Object |
| uts | Bioware Aurora Sound Object |
| utt | Bioware Trigger Data |
| utw | Bioware Waypoint Blueprints |
| utw | Unity Whirld Package |
| utx | Unreal Tournament Texture Package |
| uvx | Unreal Tournament 2003 Saved Game |
| uxx | Unreal Tournament Cache |
| uz2 | Unreal Tournament 2004 Package |
