| Extension |
File Type |
File Description |
| .u | Image | Subsampled Raw YUV Image (Most common) |
| .u | Image | Subsampled Raw YUV Image (Most common) |
| .u3d | Image | Universal 3D File |
| .u3i | Text | U3 Application Information File |
| .u3p | Executable | U3 Smart Application |
| .uax | Game | Unreal Audio Package |
| .ub | Audio | Unsigned Byte Audio File |
| .uc | Game | UnrealScript Class |
| .uc2 | Compressed | UltraCompressor 2 Archive |
| .uci | Backup | UFS Explorer Backup File |
| .udb | Data | Dynamics AX User Database File |
| .udf | Executable | Excel User Defined Function |
| .ufo | Raster Image | Ulead File Object |
| .uha | Compressed | UHarc Compressed Archive |
| .ui | Developer | User Interface File |
| .uibak | Disk | UltraISO Backup Disk Image |
| .uif | Disk | Universal Image Format Disc Image |
| .uis | Settings | WindowBlinds User Interface Specification |
| .ukx | Game | Unreal Animation Package |
| .ulaw | Audio | Raw ?-Law Audio File |
| .ulf | Data | Universal List File |
| .uls | Misc | NetMeeting User Location Service File |
| .ult | Audio | UltraTracker Module |
| .ulw | Audio | Raw ?-Law Audio File |
| .ulz | Data | USBlyzer Data Capture File |
| .umod | Game | Unreal Tournament Module File |
| .umx | Game | Unreal Music Package |
| .unauth | Text | SiteMinder Unauthorized Message File |
| .uni | Audio | MikMod UniMOD Module |
| .unr | Game | Unreal Level Map |
| .unx | Text | Unix Text File |
| .uop | Game | Ultima Online Patch File |
| .upd | Text | Program Update Information |
| .upoi | Data | iGO Points of Interest File |
| .url | Web | Internet Shortcut |
| .urt | Image | Utah Raster Toolkit File |
| .usa | Game | Unreal Saved Game File |
| .usf | Audio | Nintendo 64 Music File |
| .usflib | Audio | Nintendo 64 Song Library |
| .usx | Game | Unreal Static Meshes |
| .ut2 | Game | Unreal Tournament Map |
| .ut2mod | Game | Unreal Tournament 2003/2004 Module File |
| .ut3 | Game | Unreal Tournament 3 Map File |
| .utc | Game | Bioware Creature File |
| .utf8 | Text | Unicode UTF8-Encoded Text |
| .utx | Game | Unreal Texture Package |
| .utxt | Text | Unicode Text File |
| .uu | Encoded | Uuencoded File |
| .uud | Encoded | UUDecoded File |
| .uue | Encoded | Uuencoded File |
| .uvf | Data | Uncertain Value Format |
| .uvx | Game | Unreal Tournament 2003 Saved Game |
| .uw | Audio | Unsigned Word Audio File |
| .uwf | Audio | UltraTracker Wave File |
| .uxx | Game | Unreal Tournament Cache |
