When it comes to our energy woes, there may be a light at the end of the tunnel -- a green light, and one not powered by petroleum.

We may be able to curb our addiction to fossil fuels by using plants, animal fats and old restaurant grease. But there are a few drawbacks.

Consumers are already familiar with ethanol, a simple alcohol distilled from corn and often added to gasoline. But even easier to produce is biodiesel, a mixture of more complex molecules that can be made from all sorts of fats and oils, including leftover foodstuffs.

• Click here for more photos.

Biodiesel is safe to handle, nontoxic and biodegradable. Its proponents says it's a cleaner-burning replacement for petroleum-based fuels and that its use will greatly reduce greenhouse-gas emissions and other toxic air pollutants.

"Biodiesel could be one of the best carbon-mitigation processes available today for heavy-duty vehicles like trucks and buses," says Jenna Higgins, spokeswoman for the National Biodiesel Board, based in Jefferson City, Mo. "It works with what we have, and we don't have to wait for new technologies to use it."

The concept of biodiesel is surprisingly old. In the 1890s, Rudolf Diesel envisioned vegetable oil as a fuel source for his engine. In 1900, the diesel engine was demonstrated at the World Exhibition in Paris, France, running on peanut oil.

Biodiesel can be used "neat" in a formulation known as B100 (100 percent biodiesel), or blended with petroleum diesel. A 20 percent blend is called B20. The Department of Energy says B20 reduces a diesel engine's carbon-dioxide emissions by 15 percent, and B100 by more than 75 percent.

And carbon dioxide released by biodiesel combustion is offset by the carbon dioxide sequestered while growing the soybeans and other feedstock.

Yet biodiesel almost sounds too good to be true -- and many experts say it is.

"Biodiesel is, of course, made from vegetable oils that are food crops, such as palm and soy, which have played a significant role in deforestation," explains Jimmie Powell of the Arlington, Va.-based Nature Conservancy. "Dramatically expanding production to meet new demand for biodiesel would not only continue to worsen the problem, it would also have severe impacts on food prices in the developing world."

In some places, current crops can't keep pace with the bio-materials needed for producing biodiesel. Even though biodiesel is undoubtedly greener than traditional petroleum-based fuel, there's little or no regulation on how and where it's produced.

Palm oil, for example, is commonly used for cooking and as an additive in foods. Growing it has been big business in Southeast Asia since the mid-19th century, and it's only getting bigger.

Between 1995 and 2005, nearly 8.6 million acres of land in Indonesia, including vast tracts of forests and peat bogs, were converted to palm-oil plantations, more than doubling total plantation area, according to a recent report by Credit Suisse.

Tropical forests help remove millions of tons of carbon dioxide from the atmosphere every year. Burning and clear-cutting these forests to grow biofuel crops not only eliminates one of the planet's own natural air-filtration systems, but the process of land clearing itself releases even more carbon dioxide into the air as smoke or gases released during the decomposition of forest waste.

"It's unfortunate these practices give biodiesel a bad name," says Robert McCormick at the DoE's National Renewable Energy Laboratory in Golden, Colo. "There are plantations that are sustainable."

According to the National Biodiesel Board, a vast majority of the feedstock used to make biodiesel in the United States is grown responsibly and sustainably. Most of the domestic stock comes from soybean oil, mainly because the U.S. is the world's largest producer of soybeans.

"Sixty-five percent of all biodiesel used in this country comes from soybeans," explains Victor Bohuslavsky, executive directory of the Nebraska Soybean Board, based in Lincoln, Neb. "Eighty-six percent of soybeans produced was used in food. We can find good uses for the balance, and biodiesel is one of them."

Most experts agree that biodiesel is a good alternative to imported petroleum, despite the complications.

"It's not an easy problem to solve, because we've built our entire system around coal and petroleum," explains Kert Davies, research director for Greenpeace. "We have to be creative and look at a diverse set of solutions to solve our addiction to oil."

The DoE's McCormick agrees.

"Using biodiesel is not going to end petroleum imports," he says, "but it is an important part of the solution."