The mileage you get can vary widely on how your drive. For example, after you fill up, accelerate hard every time you start from a stop or need to get up to speed (as long as you do so safely of course). After measuring your mileage for that tank of gas, accelerate as slow as you safely can for the next tank of gas. There will be a significant difference.
Or, underinflate your tires by 5psi, then inflate them fully and there will be a distinct improvement.
This year the EPA changed the way they measure mpg to more closely reflect real life conditions. Previously almost no one got the mpg listed by the EPA.
We typically beat the EPA listing by a couple of mpg. I have heard of people termed 'hypermilers' who tend to get quite a bit over the listed mpg, however some of what they do to get there is not recommended by safety eperts
