The Ford Flex-Fuel engines will run on various blends of Alcohol-Gasoline mixures from standard gasoline and a alochol/gasoline mixture of up to 85% ethynol alcohol.
There are pros and cons for each fuel depending upon the availability and price in your area. Alcohol will yield 20%-25% less MPG than with regular gasoline, but that can vary from the blend of gasoline used in your part of the country and even from summer to winter blends may vary.
If you have the Flex-Fuel engine and the E85 fuel is available, give it a try and see how your Sport Trac performs and make a note of your MPG vs price and see if you get any savings. Also, give us a report of your findings after a few tanks.
...Rich