Flex Fuel also known as E85 (Blended 85% ethanol and 15% gasoline) can be used in approximately 11 million vehicles today. It current runs about 60 cents per gallon less than regular gasoline.
Some drivers have a Flex Fuel vehicle and do not realize it, so you can check under your fuel door and look for the E85 Label or the Yellow gas cap. Other vehicles have a badge with the term E85, Flex Fuel or FFV.
E85 provides fewer miles be gallon (less energy content), so you fill up more frequently. FFVs typically get about 15% to 27% fewer miles per gallon when fueled with E85. As a rule, E85 would have to be priced 30% less than gasoline for you to save money. You should test this on your own Flex Fuel Vehicle and do the math to confirm if the numbers work for you.
You may also have trouble finding E85 and a gas station near you. There are approximately 2400 Stations that carry Flex Fuel across the US. Many are located in the upper Midwest.
My 2014 Chevrolet Captiva is rated for 24 MPG combined City/Highway using Regular Gasoline and only 18 MPG combined City/High when using E85. It costs me about the same to run gasoline versus E85, so in my case there is no actual savings.