Are you arguing how the sentence is worded? I would take 10% ethanol added to mean it was 10% ethanol 90% gas. For ten gallons you would have 1 gallon of ethanol and 9 gallons of gas.

If that is not the case how do you calculate this? With gas I get 25 MPG so 10 gallons of gas I can go 250 miles. With 10% ethanol it takes 11 gallons to go 250 miles (10% more fuel). The 25 mpg is now 22.7 or 10% less.

BTU content of dry ethanol is aproximately 75% of that of Gasoline for the same volume. BUT, alcohol is also hygroscopic. So the BTU content can actually be quite a bit less, by the time it used. Regular Gasoline these days is supposed to be 90% gasoline, 10% Ethanol. It might actually be 85% gasoline, 10% ethanol, 5% water.

E85 can be far far worse. It is supposed to be 85% ethanol, 15% gasoline. It might be 30% water.

And the taxes are based on gallons, not BTU content. So, yep, you get double screwed.

Welcome to how our government screws things up.

What I'm trying to say, is that, you would only get a 10% decrease in mileage if the ethanol in your example had zero BTU content...

using a 75% equivalence to gasoline, and assuming that BTU content is directly related to fuel efficiency, a 10% blend would only decrease mileage by 10% x 25% = 2.5%, yielding 24.375 MPG

That is alot less than the 10% claim from masrum, hence my confusion...

I knew someone whould chime in with a nice ME thermodynamics answer, thanks Red Beard! Thermodynamics..........*shudder*.