I've experienced the opposite - In my car, 10% ethanol results in a 10% decrease in gas mileage.
The ethanol-free stuff I like to burn is 91 octane and when I have to buy with ethanol it's 87, but I don't think that makes much of a difference.
Pure-gas.org also has an iOS app.
I get
slightly higher fuel mileage when I use 91-octane ethanol-laced gasoline, but about a 10 percent increase when I use ethanol-free 91-octane gas, when I can get it. But if I move up to 93 octane ethanol-free, there's no improvement over 91 octane ethanol-free.
If mixing 10 percent ethanol reduces mileage by 10 percent, then it seems to me that the ethanol basically takes up space, while providing little or no energy. So what good is it, and why does Big Brother insist that we use it, except for the obvious reason of the Iowa Caucus?
I also experience an immediate 10 percent reduction in gas mileage the day the "winter blend" fuel starts flowing. I'm not sure what's different about the "winter blend," but whatever it is certainly kills my mileage.
I should mention that the car I'm using as a reference has a non-functional fuel gauge, so I use the trip odometer instead. Because of that, I'm very much aware of the car's MPG. I just look at the odometer and divide it by how much fuel I just pumped, and there you have it. With ethanol-free fuel, I get about 25-26 MPG. With ethanol-laced summer blend, I get about 22-23. With ethanol-laced winter blend, about 20 - 21.
-Rich