I was wondering if the winter gas formulation which in my state is around 10% Ethanol affects gas mileage. I drive mainly in the city and use to average about 18.2 mpg and since a couple of months ago it's been declining, as of today it's about 17.7 mpg. I know it isn't a big difference. I'm just wondering if the winter formulation affects gas mileage. My car still runs the same and I have not seen any change in performance. Thank you.