My car drives fine with it, but i can definitely tell a difference in gas milage. On the interstate i usually get 17 to 18 mpg with premium gas, with premium and 10% ethanol, i get 14.5 to 15.5 mpgs. I tested this driving to baton rouge from new orleans and also driving to houston every other week. Also with the 10% ethanol, my stop and go mileage is a disgrace.