I did one last final test - this is not for starting a battle of formats, I'm just very interested in these things from a technical point of view... (apologies to Jim... :-) The "overlay" feature of RAR seems to have a real disadvantage - it does not improve compression at all... I took 4 identical copies of the same huge text file and compressed it as SIT and RAR - guess what? SIT was still smaller. This means that RAR is not a "version history" format that calculates deltas between files, it really only re-uses some internal tables. This might give a positive result in just one (very special) case: If you have a set of files where each is constructed out of some few large identical blocks that repeat itself across the whole set of files. This is something that you can easily construct (by setting up files to give maximum results against the other formats), but it's something that you will never see in the real world, I'm afraid. I'm also very disappointed about the compression options - the default "best guess" is already the end of the story - although everything else is either faster or slower, it typically gives larger files in the end, up to twice the size of even ZIP! Looks like StuffIt will stay monopolist for yet some more time... :-)