I let my wife drive the ISF during the week because it is the only comfortable vehicle we have (others are S2000, lifted Dodge Ram, and Honda CBR1000RR). She averages about 80 mph, mostly highway driving, and has bouts of spirited driving. When she is driving, she averages about 20-21 mpg. When I get a hold of it on the weekends, the gas mileage goes down to 18-19, but that is more city driving, and I get on the throttle more often. On an average week, we get 300 miles per tank.