The 85-percent-ethanol, 15-percent-gasoline mixture called E85 may not live up to its hype. While it does appear to reduce emissions as claimed, you get worse fuel economy: So poor that using $3-a-gallon E85 would be like burning $4-a-gallon regular gasoline, says Consumer Reports.

That assumes you can even find E85. In its October 2006 issue, the magazine states that E85 is mostly distributed in Midwestern states, closer to the cornfields that provide much of the organic matter that is distilled into non-drinkable ethanol, or grain alcohol. Of the 175,000 gas stations nationwide, fewer than 1,000 pump E85. (For a list, see the National Ethanol Vehicle Coalition's Web site). New York State, for instance, has only two stations, and New England has none at all.

In a test of a 2007 flex-fuel Chevrolet Tahoe, Consumer Reports found that overall economy with E85 fell from 14 mpg to 10 mpg (29 percent), acceleration of 0-to-60 mph improved from 9.1 to 8.9 seconds (2 percent), and nitrogen oxide emissions fell from 9 parts per million to 1 ppm (89 percent)—although hydrocarbon emissions remained unchanged at 1 ppm, and carbon monoxide was unchanged at a measured 0 ppm.

Automakers incur a cost in building flexible-fuel vehicles, which can run on anything from pure gasoline to the most commonly sold gasoline, already about 10 percent ethanol (in that mix, ethanol acts as an oxygenate to reduce smog), to E85. Higher-quality fuel-line fittings are required, because ethanol is corrosive (and that's why you shouldn't ever use E85 in a vehicle that isn't flex-fuel certified). The cost is an estimated $200 per vehicle. Getting E85 to the consumer also costs more: Because it's easily contaminated (ethanol soaks up moisture), it can't be transported through existing gasoline pipelines and has to travel by more costly rail, truck, or barge.

There's also a benefit, however: The government lets flex-fuel vehicles pretend they get two-thirds better mileage than gas-engine vehicles, even though actual mileage numbers are worse. A Tahoe that gets 21 mpg (highway) is actually rated at 35 mpg, for purposes of calculating the Corporate Average Fuel Economy rating, currently 27.5 mpg for cars and 21.6 mpg for light trucks. And that's for a vehicle whose best observed economy, highway-only driving, was measured by Consumer Reports at 15 mpg with E85 (and 21 mpg with gasoline). The EPA fuel-economy number that appears on the window sticker of a flex-fuel car is its gasoline mpg rating, not the E85 calculation.

Others have noted additional issues with ethanol-based fuels, starting with the problem of whether the U.S. can actually grow enough corn to feed the country, produce ethanol for the 10-percent oxygenate-blended gasoline, and create significant quantities of E85 fuels. To grow enough corn (or other crops) to run all vehicles on E85, Popular Mechanics said in its May 2006 issue, the U.S. would need to repurpose two-thirds of its 938 million acres of farmland. And a debate is ongoing about the net energy balance of ethanol—the amount of energy in a gallon of ethanol fuel minus the energy used to raise crops, transport them to an ethanol distillery, and then get the finished product to the customer. Studies have produced numbers ranging from a 30 percent loss to a 40 percent gain; most report a positive energy balance of 20 percent or more, using current production techniques.

To read more about alternative fuels, click here.

To read about moonshine fuel, click here.

For our review of the Chevrolet Tahoe, click here.