E15 Gas Introduced, Car Mfgs Warn Not To Use It

mpierce wrote:

The ethanol is 10% less energy per gallon than gas. There is a 10% mix. So, 10% of 10% means there is 1% less energy per gallon.

I think your numbers are a little off. Gasoline contains ~114,100 BTU's per gallon. Ethanol contains ~76,100 BTU's per gallon.

That means Ethanol contains 66.67% of the energy of gasoline, not 90% less.

In the case of E15 then you would be losing ~15% of the energy per gallon.