E10 Ethanol and Fuel Mileage

Visit any of the internet discussion forums where ethanol is being discussed and you will always see someone claiming large decreases in fuel mileage with ethanol blends. The problem though with user testimonials is that there is no way to control the other variables that effect fuel mileage in normal day to day driving. That is why formal tests conducted under controlled conditions is the only way to truly measure the effects of ethanol blends on fuel mileage.

Some time back California decided that they needed to move to lower carbon fuels. The move to greater use of biofuels in the transportation sector was part of this strategy and in preparation they started conducting tests to determine how the expanded use of ethanol would effect emissions. One of the studies conducted also reported the effects of ethanol blends on fuel mileage.

Fleet average fuel consumption increased by 1.4% when ethanol content was increased from the zero to the high level.

In this case the high level that they refer to is 10% ethanol. So in formal testing where other variables that could effect fuel mileage are controlled E10 increases fuel consumption by 1.4%. Putting that a different way, if a vehicle gets 30 miles per gallon on straight gasoline, the same vehicle should get about 29.6 miles per gallon on E10 if all other variables other than fuel selection are eliminated.

Source : Effects of Ethanol and Volatility Parameters on Exhaust Emissions