It's possible that your archive may be in .tar.bz2 format. Archives with this extension have been compressed with bzip2. Bzip2 generally compresses significantly better than gzip. Its only disadvantage is that compression and decompression are slower, and bzip2 consumes more memory than gzip while running. For modern computers, this isn't much of an issue, which is why you can expect bzip2 to become more and more popular as time goes on.

Because bzip2 has been gaining popularity, many Linux distributions come with versions of tar that have been patched so that passing a y or i option will inform tar that the archive is in bzip2 format and needs to be automatically decompressed with the bzip2 program. To see if you have a patched version of tar, try typing:

$ tar tyvf archive.tar.bz2 | more

or

$ tar tivf archive.tar.bz2 | more

If neither of these commands work (and tar complains of an invalid argument), there is still hope -- read on.