The 450 I demo'd got somewhere between 50 and 60mpg, which impressed me mightily. On the 500, my first and second rides were about 30 miles each, and I figured I would not refill between them to get a better baseline on mileage. This was all technical singletrack, my old carb'd 450 gets about 35 in this use. After 64 miles: (note the fuel level). It ran to the truck, but would not restart. Guess I shaved that close! And just filled it up at a pump: So I believe the usable capacity of the 500 is 2.2 gallons. I'd heard a variety of figures, thought I'd post my experience as a baseline. Now, what remains to be seen is why I got 29.5 miles per gallon (I was even being somewhat nice, during break in), when that is so far from what I got on the 450.