A recent "tip of the day" from Unix Guru Universe noted:
In HP Unix, the compress command will compress around 50 to 60%. gzip will compress the file up to 80%. There is a command available in HP's unix to convert a compress file to a zip file. znew will automatically convert compressed files (*.Z) to gunzip files (*.gz).I wondered if this existed under OS X and by doing a which znew, I found that it does indeed exist under /usr/bin/znew. The man page states, "Znew recompresses files from .Z (compress) format to .gz (gzip) format. If you want to recompress a file already in gzip format, rename the file to force a .Z extension then apply znew." What a handy little program!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040416203902218