Reading the labels is important but most of the time it does not give you a complete picture of what you are getting from the pump. I know that people on here will talk about the fuel mileage they got yet they have no idea how pure the fuel was when they filled up. Most labels, like ethanol and methanol, will list the MAXIMUM amount of ethanol as 10%. That means that it could be 10% or it could be 1%. I would guess that the bio-diesel is the same thing. You may have 30% or you may have less, depending on what was in the large storage tank when the new fuel was added. Without knowing the exact percentage of additives to the fuel, it is next to impossible to come up with an accurate fuel mileage figure.