Make sure your odometer is calibrated for true distance. If you go by indicated distance you are in for significant error. Your fuel fill also has to be calibrated. Start with a topped off tank. After your run, retop with calibrated fuel fill. Gas station pumps are not accurate enough. Engine tune, tire pressure, tires & wheels, axle ratio, road grade, road surface, altitude, temperature, cargo load, engine tune, clogged air filter, etc. are going to have an effect on mileage. There are so many variables it is irrelevant to compare your car with others except in general terms. It should be noted that even at .00 an hour, fuel is a minority percentage of vehicle operating costs. Most young people pay much more for insurance and depreciation. Add in maintenance and taxes, the fuel cost DIFFERENCE among models becomes fairly trivial