Quote Originally Posted by F6Dave View Post
When it comes to mileage, what matters is how much energy is in the fuel you use. Here are a few numbers:

Diesel #2: 129,500 BTU/gal
Regular gasoline: 114,100 BTU/gal
E10 gasoline: 111,836 BTU/gal
E85 ethanol: 81,800 BTU/gal
Pure ethanol: 76,100 BTU/gal

The numbers say that ethanol free regular (87 octane) gasoline has about 2% more energy than an E10 blend. So you should see roughly a 2% improvement in mileage by switching from E10 to pure gasoline. That's less than 1 MPG in my case, and given the normal variations in my mileage I haven't really noticed a difference.

BTW, 91 octane premium actually has slightly less energy content than 87.
Information like this that people post is one of the things I love about this board. I'm continually amazed and further educated by the knowledge that is shared here.