Just figured my mileage on my 1995 Buick for our trip to California. 

I tried using non ethanol gas for part of the trip.*  I've never run anything but ethanol in the Buick for the last 100,000 miles.  But on here a number of people claimed that regular gas gave better mileage.  I didn't see any improvement.  Zilch.  I tried for 3 fills to give me a reasonable amount of data.  The rest of the trip if ethanol was available that's what I used.

The disappointing thing is if I buy a newer car I'm probably not going to improve my mileage unless I get some smaller car with less comfort.

*Flat land of Iowa and Nebraska, not the mountains.