Ill just say my car gets 15mpg at 80mph. I just know I don't get 17 or more mpg going 60. Perhaps its the way my carburetor is tuned? Or it being out of tune? I know I have a vaccume leak under the hood somewhere because I can hear it, but it doesnt effect the way the car drives so I dont bother with it. Maybe that is it? But im not going to bring up silly things like perpetual motion as Caferacerx did. If you'd like pictures of the fuel guage before and after one driving 80mph and one driving 60mph after each trip, ill be happy to do it.