I picked up a 2011 Ford Crown Victoria Police Interceptor, which is a flex fuel vehicle. I am going to keep track if its mileage on E85. This is primarily a work vehicle and it gets driven to work on suburban roads and highway, about 50-50 mix.
Today it was at 105619 miles, the last fillup was at 105337. I filled up with 18.423 gallons of E85 @ $1.759 / gallon. That works out to 15.3 miles per gallon.
Premium was at $2.45 per gallon today, for a savings of $12.16 per tank.
At some point I will keep track of my mileage on regular unleaded to see how much of a mileage hit I take on E85. It might be as high as 5 mpg, we will see.