[Gerry Zagorski]

This from a automotive website

These days more than 95 percent of gas sold is E10, said AAA spokesman Michael Green. E10 is 10 percent ethanol and came into use after amendments in 1990 to the Clean Air Act, according to the Department of Energy. All cars are certified to run the stuff; in fact, it's difficult to find ethanol-free gas anymore.

Yet the more efficient ethanol-free blend is what the EPA uses to produce gas mileage figures posted on that new-car sticker.

And there's the problem. Ethanol's lower energy density leads to worse gas mileage, which is why using E85 (85 percent ethanol) in cars that accommodate it is usually a bad idea. The math carries to E10, which has up to 10 percent ethanol. A gallon of E10 has 96.7 percent of the energy in one gallon of gasoline, according to the DOE's Alternative Fuels Data Center.

That means E10 fractionally lowers real-world gas mileage. How much? Try about 3 percent, said Toyota Senior Energy Researcher Mike McCarthy and Ford powertrain spokesman Paul Seredynski. AAA's Green and the EPA both pegged the E10 loss between 3 and 4 percent. That means a car that sports a 30 mpg EPA combined figure is already hampered from achieving that number. The starting line is really 29 mpg.