I'm not sure I stayed around 65mph, I drive slow because I'm used to big trucks, and Semis. I'd like to think my VX is special in that respect, I know it's a thirty little car but this one has so far been not too bad. I try to stay at lower rpm's, the car is bone stock as well if that makes any difference. Factor in human error as well, when I go to AZ this weekend I''l find out definitively, it's a 20 gallon tank right?