inetinfo virtual memory behavior

Hi, I have a question about IIS process Inetinfo's memory behavior. Over the
course of two days, the perfmon process,virtual bytes counter grows from 1G
to 2G at which time out of memory errors are thrown and the server is
restarted.

However, during this time, private bytes and working set grow only from 500M
to 600M. Committed bytes grow from 1.1G to 1.3G, and available bytes goes
from 2.5G to 2.2G.

My question is why virtual bytes might grow so much quicker than the other
counters. My only theory is that there could be a slow memory leak, whose
pages in RAM are not active and so eventually moved to the paging file, thus
showing up in the virtual bytes but not the working set. But wouldn't the
leak then show up in committed bytes and available bytes? Is this behavior
consistent with a slow memory leak, or is another theory more plausible.
Thank you.