I supposedly have a 31gal tank in my f-250. I had to have my tank removed, so I ran it down to where it said 3 miles to empty. We got just shy of 2 gallons out of the tank when we dropped it. When it was reinstalled, I drove less than a mile to a station. I could only put in 28.7 gallons! I think that sometimes they put in any tank that they can get at a good price. I actually think that I got a leftover 29 gal tank from a previous model year. It only becomes a big deal when I am towing my camper and getting 7 MPG!