Hollywood Reporter has a list of all 2005-2006 TV shows, ranked by viewership. The Office comes in at #67 out of 156 shows.
You can find the complete list here, and the accompanying story here, which describes the upcoming Thursday 8pm timeslot as an especially competitive one.
It will definitely be interesting to see how My Name is Earl and The Office fare against its rivals …
Thanks to TV Squad for the tip.