Ethanol and Fuels Like E85
1.5 gallons of ethanol has the same energy content as 1.0 gallon of gasoline.
The energy content of 1.0 US gallon of ethanol is 76,100 BTU, compared to 114,100 BTU for gasoline. (see chart above)
A flex-fuel vehicle may experience as much as 25% lower MPG when using E85 (85% ethanol) products. This is in part because the engine's compression ratio is fixed mechanically and electronic sensors can only modify the timing of the spark and/or instruct the fuel injection system to provide more of the reduced energy-content fuel.
A 2006 University of California Berkley study, after analyzing six separate studies, concluded that producing ethanol from corn uses much less petroleum than producing gasoline.
Read more about this topic: Gasoline Gallon Equivalent