Supporters of ethanol use say it's a cheaper, cleaner burning fuel. They claim the 10% blend has virtually no impact on fuel efficiency, but some mechanics disagree.

"It's about 4-5% based on the numbers," says Mark Block, owner of Block Automotive in Cordova.

Block says it's simple science. He says a car must burn more ethanol to create the same energy as gasoline. So if you remove 10% pure gasoline and replace it with ethanol, the fuel won't burn the same.

According to Block's numbers, the driver of a vehicle that gets 20 miles per gallon would see his fuel efficiency drop to 19 miles per gallon on average.