For example, the flex-fuel 2010 Chevrolet Impala equipped with a 3.5-liter V-6 engine gets an EPA-estimated 18/29 mpg (city/highway) on gasoline and 14/21 mpg when burning E85. The acceleration is pretty much the same, but the car's range is shortened. In other words, you'll be filling the tank more often when using E85.

Do the math and you'll discover that E85 must be priced roughly 28 percent less than gas just to break even. For example, if gasoline is $3 per gallon, E85 would have to be priced below $2.16 per gallon. There are regions in the Corn Belt where E85 reaches this threshold, making it cost effective.

How available is E85 fuel?

On a national level, E85 is hardly widespread. The highest concentration of filling stations is in corn-growing states such as Illinois, Iowa and Minnesota. Overall, there are roughly 2,100 E85 stations across 44 states, according to the U.S. Department of Energy. Availability remains poorest in the South and the Northeast -- where it's hard to produce ethanol locally.

So where is the benefit?

The 2011 Nissan Armada is flex-fuel capable, one of the few models from Japanese automakers.

The best reasons to buy an E85 vehicle are to decrease U.S. dependence on petroleum -- which is non-renewable and comes mainly from foreign countries -- and to keep more of your money in this country.

E85 also has environmental benefits, although the degree is in question. A flex-fuel car burning E85 has different levels of tailpipe pollutants, but it's not dramatically better overall than gasoline exhaust. Separate from true pollution emissions, E85's output of carbon dioxide -- a greenhouse gas -- is again comparable to that of gasoline, at the car's tailpipe. The theoretical benefit is that the carbon in ethanol comes from corn plants, which, in a sense, recycle the carbon.

In comparison, petroleum is carbon that was trapped underground for millions of years before being released into the ecosystem. The National Ethanol Vehicle Coalition says E85 reduces CO2 by about 36 percent to 42 percent versus gas. Still, scientists point out that petroleum is used to plant, fertilize, harvest, process and transport E85.

Will E85 prices come down?

Ethanol prices are already subsidized in some states. Buyers in Illinois pay no sales tax, which brings down the posted price per gallon (tax is included in per-gallon prices for straight gasoline, not added on top of the total). Price hinges on supply and demand and economies of scale. Demand recently jumped when the additive MTBE was found to be polluting groundwater. States that used MTBE are switching to ethanol as an octane booster and oxygenate, which reduces summertime air pollution from gasoline evaporation.

Ethanol proponents say an oft-cited study that claimed ethanol takes more energy to produce than it gives back is no longer accurate. According to NEVC, the overall energy advantage over gasoline is 3 to 1. This ratio is expected to reach 9 to 1 when the industry moves away from food crops and toward waste vegetation and/or plants that are simpler and cheaper to grow, harvest and process. Switchgrass, which President George W. Bush mentioned in one State of the Union address, is one such plant.

As alternative fuels go, biofuels like ethanol and biodiesel have great advantages in the real world. They can be distributed and dispensed like conventional liquid fuel, and used in vehicles that cost automakers very little in terms of additional cost. The same cannot be said of hybrids, which force consumers to pay a higher sticker price.

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