I drive 70 mi. to work every other day. I always have my cruise control set at 70mph. Here is a chart of my MPG since I've owned my car. Most of my tanks are 1:3 city to highway driving. Numbers don't really agree with Janizary's but i do keep my tires inflated at 38psi and calculate my mpg using the trip odometer (I always reset the trip at the pump and refuel the same way) . With an Si.