David: The exact command this time was a "tar jxf linux-2.6.23.tar.bz2" as part of an emerge (gentoo). Gnu tar version 1.18 but has happened with prior versions too. I replicated it after my post by manually untarring it on the command line and can almost always replicate the problem with any large (GCC/kernel) tarball. If I shut down all other processes, the untar will go longer but eventually the oom-killer will be invoked.