The only time I tested my Contour's gas mileage was when driving it home 300 miles just after I bought it from my brother-in-law.
On that trip -- all freeway at about 65 mph -- it seemed to get 35 mpg as I calculated it when filling up. I was very happy!
However, when I told my nephew (the previous driver) I got 35 mpg, he said that he had NEVER gotten that kind of mileage even on the highway. So maybe I calculated wrong.