from my experience...those guy are FOS....I don't know how they figure mileage, but if they aren't filling up to the exact same spot each time it isn't a consistant way to calculate mileage. (you could fill up with a gallon or 2 less depending on how you fill your tank) If you do not actually ride with them...I find anyone's mileage claims hard to believe. I bought a diesel because of all the mileage claims that I have heard from my friends. Well, the mileage isn't bad compaired to my old gas truck, but it is about 5 mpg off of what they claimed. I am happy none the less. Stanadyne does good with anti-gel....I should know....I live in Alaska and use it with almost every tank year round. I have not seen a mileage increase from it though...just piece of mind. I have also used the power service additive when I could not find stanadyne. Worked good, no mileage increase though.