.UPK File Extension

File used by Unreal Engine 3, a free gaming engine used to develop popular games such as Unreal Tournament 3, Mass Effect, Mirror's Edge, and BioShock; serves as a file container which includes various types of game files; may contain 3D models, textures, maps, music files, game settings, and other files.

UPK files are used to load on-demand content while playing a game. They can be created and edited using the Unreal Development Kit (UDK).