| .U | Epic Games | Fichiers de jeu | Unreal Tournament Class Package | Dragon UnPACKer | Open Source |
| .U8 | Nintendo | Fichiers de jeu | Mario Kart Wii Archive File | Wiimms SZS Toolset | Nintendo |
| .UBI | Ubisoft | Fichiers de jeu | Ubisoft Logo Animation | Unknown Software | Unknown Developer |
| .UC | Epic Games | Fichiers de jeu | UnrealScript Class | UnrealEd | Epic Games |
| .UCL | Tripwire, Inc. | Fichiers de jeu | Killing Floor System File | Killing Floor | Tripwire Interactive |
| .UCM | FAKT Software | Fichiers de jeu | Crazy Machines Model File | Crazy Machines | FAKT Software |
| .UCS | Relic Entertainment | Fichiers de jeu | Relic Localized Unicode Strings | Homeworld 2 | Sierra Entertainment |
| .UDM | Motcreations Software Inc. | Fichiers de jeu | MapView User-Defined Module File | MapView Virtual Gaming System | Motcreations Software Inc. |
| .UFO | Ulead Systems | Fichiers de jeu | Ulead File Object | Ulead Photo Express | Ulead Systems |
| .UGI | Paterva | Fichiers de jeu | MultiGo Game Data | MultiGo | Paterva |
| .UH | Ensemble Studios | Fichiers de jeu | Age Of Empires II (The Age Of Kings) File | Age of Empires II | Microsoft Corporation |
| .UHTM | Epic Games | Fichiers de jeu | Unreal Tournament Data File | Unreal Tournament | Epic Games |
| .UKX | Epic Games | Fichiers de jeu | Unreal Animation Package | Dragon UnPACKer | Open Source |
| .UMAP | Epic Games | Fichiers de jeu | Unreal Engine Map File | Unreal Tournament | Epic Games |
| .UMD | Ubisoft | Fichiers de jeu | Splinter Cell Blacklist Game Data File | Splinter Cell Blacklist | Ubisoft |
| .UMOD | Epic Games | Fichiers de jeu | Unreal Tournament Module File | Unreal Tournament | Epic Games |
| .UMV | Viacom New Media | Fichiers de jeu | Are You Afraid Of The Dark? Video Data | Are You Afraid of the Dark? The Tale of Orpheo's Curse | Viacom New Media |
| .UMX | Epic Games | Fichiers de jeu | Unreal Music Package | VLC Media Player | VideoLAN |
| .UNF | Open Source | Fichiers de jeu | UNIF ROM File | Nestopia | Open Source |
| .UNR | Unreal Software | Fichiers de jeu | Unreal Level Map | UnrealEd | Epic Games |
| .UPK | Epic Games | Fichiers de jeu | Unreal Engine 3 Package | Unreal Tournament | Epic Games |
| .UPS | Open Source | Fichiers de jeu | UPS Patch File | MultiPatch patching tool | Open Source |
| .UQM | Toys for Bob | Fichiers de jeu | The Ur-Quan Masters Archive File | The Ur-Quan Masters | Toys for Bob |
| .USA | Microsoft Corporation | Fichiers de jeu | American English Localization Language File | Microsoft Notepad | Microsoft Corporation |
| .USX | Epic Games | Fichiers de jeu | Unreal Static Meshes | Dragon UnPACKer | Open Source |
| .UT2 | Epic Games | Fichiers de jeu | Unreal Tournament 2003/2004 Map | Unreal Tournament | Epic Games |
| .UT2MOD | Epic Games | Fichiers de jeu | Unreal Tournament 2003/2004 Module File | Unreal Tournament 2003 | Epic Games |
| .UT3 | Epic Games | Fichiers de jeu | Unreal Tournament 3 Map File | Unreal Tournament | Epic Games |
| .UT4MOD | Epic Games | Fichiers de jeu | Unreal Tournament 2004 MOD Installation Package File | Unreal Tournament 2004 | Epic Games |
| .UTB | Unknown Developer | Fichiers de jeu | µTBackup Backup | µTBackup | Unknown Developer |
| .UTC | BioWare | Fichiers de jeu | BioWare Aurora Game Engine Creature Data File | Various video games | Various Developers |
| .UTD | BioWare | Fichiers de jeu | BioWare Aurora Game Engine Door File | BioWare Neverwinter Nights | BioWare |
| .UTI | BioWare | Fichiers de jeu | Bioware Aurora Item Data | BioWare Neverwinter Nights | BioWare |
| .UTP | BioWare | Fichiers de jeu | BioWare Aurora Game Engine Placeable Object File | BioWare Neverwinter Nights | BioWare |
| .UTS | BioWare | Fichiers de jeu | BioWare Aurora Game Engine Sound File | BioWare Neverwinter Nights | BioWare |
| .UTT | BioWare | Fichiers de jeu | Bioware Trigger File | BioWare Neverwinter Nights | BioWare |
| .UTW | BioWare | Fichiers de jeu | BioWare Aurora Engine Waypoint File | BioWare Neverwinter Nights | BioWare |
| .UTX | Epic Games | Fichiers de jeu | Unreal Texture Package | Dragon UnPACKer | Open Source |
| .UV2 | Electronic Arts | Fichiers de jeu | Jane's Combat Simulations: F-15 Game Data File | Jane's Combat Simulations: F-15 Game | Electronic Arts |
| .UVX | Epic Games | Fichiers de jeu | Unreal Tournament 2003 Saved Game File | Unreal Tournament 2003 | Epic Games |
| .UXX | Epic Games | Fichiers de jeu | Unreal Tournament 2003 Cache File | Unreal Tournament 2003 | Epic Games |
de 1 
