Good information, till222. There will be quite a bit of variance based on:
-Elevation above sea level
-Temperature
-Ethanol content in your gas (varies by area/time of year)
-Octane of your gas (91 is pretty much 'max' on west coast, with 95+ moving east)
-Tire Pressure (remember that just a few lbs of difference can make an impact to your MPG)
-Vehicle load (i.e., how much load weight is the vehicle carrying, 1-125lbs passenger vs. 1 250lb passenger vs. multiples, trunk junk, etc.)
General Comments agove, not necesarrily directed to till222