The first time I filled the enormous (13.2 gallon) tank, I packed in 10.49 gallons. Over 300 miles driven (and some idling) that equates to 28.8 mpg. I do not drive like I'm on an economy run, so that mileage is fine. I have no clue of the stealership packed the tank full, the same as I, so it could be a little better.