Fed EPA mandates a certain gallon-amount be used in the fuel each year at this point. It's hard to tell without measuring which fuels have it, which ones don't, and how much each one has.
Each pump has a sticker that says "may contain up to 10% ethanol by volume" for this reason. You're never really sure. Of course, they don't tell you how much "water by volume" the fuel now contains because of the ethanol... Imagine, the gas station pays for a thousand gallons of fuel, and sells 1,100 betwen fill ups.
Looks great on the books, don't it?
__________________
"¿ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"