Sega surely loves their weird compression formats :P Anyway, this time I am trying to figure out their LZ01 compression format, and I am lost. I assume it is based off LZ77. This is the header (thanks drx): 0x00 - 0x03: 4C5A 3031 (LZ01) 0x02 - 0x07: The compressed file size (4 bytes) 0x08 - 0x0B: The uncompressed file size (4 bytes) 0x10: The start of the data So the header is 0x10 bytes long. The sliding window length is 2110 bytes (why this number, I have no idea.) The good thing is that there are uncompressed files in the DS version that are LZ01 compressed in the PS2 version (why would the PS2 versions files need to be compressed anyway?), so at least I know what the uncompressed data is. So, here are 2 files, which have a uncompressed version and compressed version: drop3ez.dat (LZ01 compressed) drop4ez.dat (LZ01 compressed) (There are a few bytes that are different between the compressed & uncompressed version, but they occur before byte 2048.) Anybody have any ideas on this compression format?