I am by no means an authority on Fuel Additives; but with the purchase of my "New to me" 03, and finding that it only gets 16mpg for the kind of driving I do. I went to searching. I found the DieselKleen and Marvel's Mystery Oil combination. The very first tank my average went from 16. 1-17. 1 mpg, to 19. 1-20. 5. Now, I know this is only my first tank, and that everyone drives different, and every truck is different. But, this evidence is enough for me to keep trying it and see what kind of benifits I get after a few tanks.