Simply put, a flex-fuel vehicle using gasoline travels farther, at a clip of about 3 miles per gallon. That’s what we discovered while driving a 2007 Chevrolet Avalanche with flex-fuel capability. We clocked an average fuel economy of 13.4 miles per gallon using regular grade unleaded – not so hot, but much better than E85. A tank of E85 gasoline registered just 10.4 miles per gallon under virtually identical driving conditions. This makes the use the E85 more expensive, by around $20 more per tank. And while that may seem like chump change, it’s exactly the opposite of what people are currently looking to accomplish.