159 active drilling rigs in North Dakota according to the NDIC website.
However, it should be noted that Rory sent me the active rig list (from the NDIC website) that clearly showed 159 active rigs on November 15, 2010, despite the NDIC saying there were still 158 active rigs.
Now, see comment below, I've been told that there were 160 active rigs on November 17, 2010, which in fact may be correct. If so, I missed it.
I'll wait for additional feedback before going to 160 as the record. The Director's Cut in December should clear it up. As noted below, on any given day there are rigs taken off the active list because they are in the process of moving, etc., so there's not question that if the "official" count is 159 rigs, in fact, the list could be longer by two or three.