With flex-fuel cars that can run on E85 ethanol still a minority of the vehicles on sale, you might think ethanol isn't as important as some other future fuels.

But up to 10 percent of every gallon of gasoline you buy today is ethanol, and that proportion may rise to as much as 15 percent if gas stations migrate to so-called blender pumps.

Congress has mandated increasing volumes of ethanol in the U.S. fuel mix, though some analysts say the rules simply can't be met.

So what exactly are the benefits--and the problems--of using ethanol as a vehicle fuel, in whatever proportion?

Click the links to check out the pros and cons of both hybrid vehicles and diesel cars.


There are many reasons to support a move away from fossil fuels, but one of the most compelling is to improve U.S. energy independence.

Though the U.S. has its own reserves of crude oil, large amounts are still bought in from politically unstable regions of the Middle East.

Reducing the use of a fuel that could suddenly dry up through trade restrictions or suddenly cost more is very much a priority, and ethanol--which is mostly produced domestically--is one way of hedging against those threats.

Large swathes of countryside, particularly in the Midwest, are set aside for the corn used as a feedstock for refining ethanol.

As demand increases, that has a positive effect on jobs. More ethanol production in the U.S. means more jobs for U.S. citizens.

Ethanol is also greener than gasoline, because corn and other plants absorb carbon dioxide from the atmosphere as they grow. The fuel still releases CO2 when you burn it, but the net increase is lower.

Potentially, ethanol is also tailor-made for newer, higher-compression engines.

A high compression ratio usually requires higher octane levels in the fuel to prevent pre-ignition, a condition that puts high levels of stress on an engine. Ethanol has a higher octane rating than regular gasoline, so it's suited to these efficient, high-compression designs.

Lastly, using ethanol as a small portion of the gasoline blend offers adaptability. Any car since 1980 has been designed to handle up to 10 percent ethanol in the gasoline, letting you run that percentage of your miles on a domestic fuel rather than irreplaceable fossil fuels.

But to go with the Pros, there are also some Cons (see next page).

Big square baler harvesting wheat straw for production of cellulosic ethanol

Big square baler harvesting wheat straw for production of cellulosic ethanol


Sadly, it's far from all good news with ethanol.

The first issue is that of fuel efficiency. Ethanol has a lower energy content than energy-rich gasoline and diesel, and as such it delivers less power when burned. While this reduces power a little, it really means higher fuel consumption and lower mileage, as the engine is less able to convert the fuel into kinetic energy.

At the moment, up to 10 percent ethanol in gasoline has little noticeable effect, perhaps 3 percent at worst. Your driving style will cause gas mileage to vary by more than that. The more ethanol you add, though, the higher the difference.

If you actually find E85 to put in the tank of a dedicated flex-fuel vehicle, your "gas mileage" will drop by 25 to 30 percent. In this case, the lower energy content really does make a difference--requiring a calculation on the cost-per-gallon of E85 versus standard E10 gasoline, and which will give you more "miles per dollar."

There are still questions over the long-term effects of E15 on regular vehicles, too. The new gasoline blends of up to 15 percent alcohol are not approved for cars built before 2001, as the alcohol can break down old rubber seals and can damage engines.

Nor is E15 approved for the host of other equipment that uses gasoline engines, from chainsaws and lawn mowers to personal watercraft and other boats.

Some carmakers advise against using E15 in their vehicles, including GM, Ford, Chrysler, and Toyota. Some new Toyota models have a red circle over the words "E15-E85" right on the gas cap. Others say that using E15 may invalidate your warranty should engine damage result.

If you're not put off by this, right now your next problem will be finding anything above E10.

At the time of writing, there's only one gas station in the whole of the U.S. dedicated to selling the newly-available E15 fuel for regular vehicles.

And only about 3,000 stations across the U.S. sell E85 at the moment--fewer than the number of electric-vehicle charging stations--and they're clustered largely in the Midwest. That compares to a total of 150,000 gas stations in the country.

Finally, there are still question marks over the agricultural impacts and real energy balance of growing crops to use as fuel.

One question: How much land should really be devoted to producing crops for ethanol, when that land is still an important resource for growing crops for food?

Another: What's the accurate net carbon footprint of corn-based ethanol? Growing it requires fuel to be burned by the tractors and agricultural equipment used to grow it, large amounts of fertilizer and pesticides, and of course transportation to fuel stations as well.

Finally, the U.S. practice of making ethanol from corn is by far the least efficient way to produce the fuel, yielding about 300 gallons per acre, compared to sugar-cane ethanol (600 gals/acre) and the theoretical promise of such future feedstocks for cellulosic ethanol as switchgrass, at up to 1,200 gals/acre.


If you want to use ethanol as a vehicle fuel today, you're already getting up to 10 percent of the alcohol fuel in your "gasoline" every time you fill it.

That percentage may slowly rise to 15 percent, but it's far from settled as to whether occasional--or regular--use of use E15 may damage cars built since 2001.

You can buy a flex-fuel vehicle, especially among full-size sport-utility vehicles and pickup trucks, and larger sedans offered by U.S. carmakers.

Your challenge will be finding E85 to put in it, since only about 2 percent of all gas stations offer it, and those stations are not geographically dispersed.

While ethanol offers numerous benefits as vehicle fuel, it comes with quite a number of drawbacks as well--and increasing its use to the levels mandated by law for the next decade may prove challenging, even impossible.

Meanwhile, you're likely buying at least a little ethanol every time you fill up with regular gasoline--making it the future fuel you're already using today.


Follow GreenCarReports on Facebook and Twitter.