On mostly open Interstate I average 27 to 28 MPG, or 300 to 350 miles before it says "E". Usually there are 2 gallons left on that range. I do very little city driving, but mileage seems to fall off pretty quick on long trips averaging over 80MPH (around 3500 RPM).
Used to get 29MPG highway before roughly 170,000 miles on the odo.
