There is only one file type that uses the .MASSEFFECTSAVE extension:
Mass Effect Saved Game
Saved game file created by Mass Effect, a sci-fi role-playing game (RPG) where players complete missions as a starship captain; contains a saved game state stored as a Zip package; used to save and load in-game progress; saved to the BioWare\Mass Effect\Save directory of a Mass Effect installation.
MASSEFFECTSAVE files may be saved automatically or manually. Auto-saves use the file naming convention profileXX_AutoSave.MassEffectSave, where "profile" is the name of the player profile, and "XX" is the number of the save. Similarly, quick saves typically use the convention profileXX_QuickSave.MassEffectSave.
To manually view the contents of a MASSEFFECTSAVE file, rename the file extension to ".zip" and decompress it with a decompression tool, such as 7zip. The two resulting decompressed files, player.sav and state.sav, can be used to modify ("mod") saved game content.
NOTE: MASSEFFECTSAVE files may be imported into Mass Effect 2, the sequel to Mass Effect.
Updated: December 22, 2009