Memphis, TN -- Eyewitness News Everywhere Uncovers drivers losing valuable miles on a tank of gas because of ethanol blended fuel.

You may have noticed a sign at the pump telling you the gas contains up to 10% ethanol, which is an alcohol and biofuel made from corn.

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. 

Block says most gas stations are now selling the ethanol blended fuel because prices have gotten so high.  He recommends drivers use 100% gasoline if they can find it.