While the appeal of a renewable, home-grown alternative to foreign oil has put ethanol front and center in U.S. energy policy discussions, the fuel still faces critics who question its feasibility as a replacement for oil and its impact on the environment.

In 2006, the United States produced almost 5 billion gallons of the fuel -- a number expected to more than double by 2009, according to the U.S. Department of Agriculture.

Ethanol is an alcohol-based fuel generally made from the starch or sugars in crops like corn, barley, sugar cane and sugar beets. Almost all of the ethanol produced in the United States comes from corn, while Brazil -- the second-largest producer of ethanol -- uses sugar cane. Ethanol also can be made from material such as wood and grasses, but the process of making it from those sources is less well-developed and more expensive than producing corn-based ethanol.

Ethanol is generally used in a blend with gasoline in the United States, and the E85 mixture -- 85 percent ethanol and 15 percent gasoline -- is available at nearly 1,200 pumps.

And that number will likely grow. President Bush called in January 2007 for mandatory alternative fuel use to grow to 35 billion gallons by 2017, and the Senate passed a bill in June 2007 requiring ethanol production to grow sevenfold by 2022.

Economic costs
But not all analysts think that ethanol is the answer to America's energy needs. The federal government supports ethanol by providing a 51 cent subsidy to refineries for every gallon of ethanol blended into gasoline.

That government support has increased pressure on corn production, driving up the cost of corn and diverting an increasing proportion of the corn crop -- an estimated 30 percent this year, according to the Department of Agriculture -- for the fuel.

The boom in corn demand is credited with revitalizing farm economies in many states, but also has sparked concerns among farmers who raise livestock and poultry, because corn is used as a feed product for these animals.

The ripples of rising corn prices have also spread beyond America's borders. In Mexico, the price of tortillas, traditionally made with corn and a staple of the Mexican diet, tripled during the latter half of 2006, according to a recent Washington Post article.

In addition, the fact that corn farmers as well as ethanol producers receive government subsidies has elicited harsh criticism from some ethanol opponents.

"It borders on fiscal insanity. We're making subsidized motor fuel out of the single most subsidized crop in America," Robert Bryce, managing editor of Energy Tribune magazine, told the NewsHour in March.

But Robert Dinneen, president of the ethanol trade industry group the Renewable Fuels Association, said that the subsidies are necessary for now to encourage continued growth. He said the subsidies would likely decrease or stop "once the ethanol industry has the market share that insulates it from the vagaries of the petroleum industry."

Questionable energy advantages
While proponents stress ethanol's benefits for reducing dependence on fossil fuels, critics say that it takes a significant amount of "old" energy sources, such as fossil fuels, to produce it. Many stages of ethanol production, such as powering farming machinery and production facilities, require energy. Producing ethanol yields about 25 percent more energy than is used in growing and harvesting the corn and converting it to fuel.

Other critics contend that there is simply not enough land to grow corn to produce enough ethanol to make a significant dent in America's fossil fuel use.

"For corn grain ethanol specifically, it is extremely limited in what it can do for offsetting our fossil fuel use," said Jason Hill, a research associate in the department of applied economics at the University of Minnesota.

A paper published last year by Hill and other researchers found that if every acre of corn grown in the United States in 2006 was used to make ethanol it would displace about 12 percent of the country's gasoline consumption.

To help solve that problem, many scientists and industry experts are pushing to develop improved technology for making ethanol from grasses, wood, agricultural waste such as plant stalks and stems, and other plant matter. This type of ethanol, called cellulosic ethanol, would allow much higher energy efficiency and wouldn't displace farmland. For now, however, making cellulosic ethanol is too expensive to be successful on a large scale.

Environmental impacts
Studies on greenhouse gas output from ethanol vary in their findings -- some finding it beneficial and some saying ethanol creates as much greenhouse gas emissions as gasoline -- in large part because of all the petroleum used to produce it.

A study published in January by University of California-Berkley researchers reviewed six different analyses and found that greenhouse gas emissions for ethanol were about 10 percent to 15 percent lower than those of gasoline. But some researchers think the effects could be even less.

Hill said studies finding reductions of greenhouse gas emissions from corn ethanol are working off the assumption that no new land is converted for agriculture, which he says is unlikely as demand for ethanol continues. Cellulosic ethanol, again, would be more energy efficient to produce and would have significantly lower greenhouse gas emissions, he said.

Meanwhile, the money to be made in ethanol is driving farmers to plant more corn and switch lands from other crops, creating other environmental concerns. This year's corn crop will be the single largest in the nation's history, according to Department of Agriculture. Some environmentalists have expressed concern that corn requires a high level of pesticides, more than other crops it may be displacing, and the process of creating more farmland to grow needed corn could also have additional environmental impacts.

Cues from Brazil?
The environmental stakes are high in Brazil as well. Brazil may be the second largest producer of ethanol, but it is the world leader in integrating ethanol into its fuel industry. Ethanol has replaced 40 percent of Brazil's non-diesel gasoline consumption and most of the cars being sold in Brazil are now flex models that can run on either gasoline or ethanol.

Achim Steiner, the executive director of the United Nations Environment Program, expressed concern in March that demand for sugar cane for ethanol could result in destruction of Amazon rainforest land if precautions weren't taken.

President Bush has been encouraging car companies in the United States to follow Brazil's lead, and cited an estimate in a speech that by 2012, 50 percent of the automobiles in America will be flex-fuel vehicles as well. By that time, Dinneen said he predicts the ethanol industry will be unrecognizable because of the changes in technology.

While Hill said he is hopeful that cellulosic technology will bring a new, more environmentally friendly form of ethanol, he cautioned that reducing energy needs will have to be a big part of solving the country's energy problems.

"We need to realize that conservation will take us so much further than finding new energy sources in the short term, and in the long term it is essential to do both," he said.

-- By Talea Miller, Online NewsHour