From a reader:

There are some great article out there about the effeciency of using corn to produce ethanol. One of the best statements I ever saw on Ethanol was straight from my owners manual for a 99 Dodge. It warned that the use of E85 would result in decreased fuel mileage of 10 -15%. If I put 15% ethanol in my tank, and get 15% lower fuel efficiency, how did we save any energy after planting, tending, harvesting and converting the corn to ethanol? For some great indepth articles find some stuff by Ed Wallace, a long time car guy and columnist for BusinessWeek magazine. Here’s one if you have the time

Correction: Several readers have made the following objection:

Your reader is somewhat mistaken on E85. E85 is up to 85% ethanol, not
15% ethanol. Also, engines that are designed for Flex Fuel now get
better mileage than the standard version of the vehicles. Considering
teh only Dodge in 99 designed for Flex Fuel was the minivan and it was
the first batch of Dodge engines designed for it. However, with all of
the energy it takes to create the corn* for the ethanol, it may not be
worth it. I’m not sure if Brazillian cane ethanol is more efficient to
make. I remain skeptical on ethanol as a fuel, but if costs can be
lowered and efficiency raised, it could be promising.

And then the same reader corrected himself:

When I said that there was slightly better mileage, I meant compared to
the amount of energy in the tank. E85 fuel has 28% less energy than
standard gas, but 25% less mileage, so on an MPJoule it’s more
efficient, but less efficient than normal gas and would have to come
down to 2/3 the price of gas to be worth it.As I said, I’m skeptical
unless we have a cheap efficient was to make it.