As Americans consume an increasing amount of the world's petroleum supplies each year, the United States has become more reliant on foreign governments for oil. According to the U.S. Department of Energy, America imports about 58% of the oil it consumes annually. Many scientists and politicians are urging a reversal of this trend, not only to reduce our dependence on foreign oil, but also to reduce the environmental damage done by our continued burning of fossil fuels. One solution to both problems could be a fuel called biodiesel.

Biodiesel is an alternative fuel that can be used in standard diesel-powered vehicles without the need to make any modifications to the engine. Unlike regular petroleum-based diesel fuel, it can be refined from any fat or vegetable oil. In America, biodiesel is produced primarily from domestically grown soybeans. This gives the fuel several advantages. First, the fuel source is renewable. Second, when consumed in a vehicle, it's much better for the environment, because it doesn't release as much black soot and carbon dioxide, a "greenhouse" gas which can contribute to global warming.

To determine just how effective an alternative fuel really is, scientists consider a fuel's so-called energy balance. The energy balance takes account of how much energy is consumed to actually make a fuel like biodiesel. For example, let's say it takes a total of three units of energy to harvest a crop, and one more unit of energy to convert the crop into useable auto fuel, for a total of four energy units. If we were able to invest those four units of energy and produce a fuel that can do six energy units worth of work in the end, then that fuel would have a positive energy balance.

David Pimental, a professor of ecology and agricultural sciences at Cornell University in New York, has studied several alternative energy sources, and gives biodiesel a good rating. "It turns out that with soybean oil, energetically (in terms of energy), you get a positive return. In other words, you get about a gallon and a half (5.7 liters) for every gallon (3.8 liters) of oil that you invest in that. So it is positive in that sense. However, the cost is significant," he says. "The data that I have indicate that it costs you about a one dollar and eighty cents per gallon (per 3.8 liters). That's for production and it's not distribution and so forth. So that is a significant price."

David Pimental is not as fond of a similar alternative fuel called ethanol, which is refined in the United States from corn, or maize, and other crop residues. For the past twenty years, Mr. Pimental has argued that ethanol suffers from a very poor energy balance, meaning it yields less energy as a fuel than is spent harvesting and producing it.

While most scientists are in agreement that biodiesel is generally a good energy investment, there may be another obstacle to its widespread adoption: the negative perceptions Americans have about diesel engines. John Farrel at the U.S. Department of Energy says that those perceptions are driven largely by aesthetic and environmental concerns. "In the early 70's in the U.S., Detroit came out with a number of diesel engines that were really not all that great," he says. "I think that there are a number of people who still associate diesel with the early 70's and those vehicles. I think the other issue is you've got a lot of old diesels running around the U.S., particularly in school buses. Because of the nature of the engine, when you take off, you see a big cloud of smoke and people associate that with diesel and nothing else."

But Mr Farrell believes that this negative perception is gradually improving. European car companies like Volkswagen are demonstrating that diesel cars can be more fuel-efficient and run cleaner at the same time. And studies have shown that biodiesel fuel can help reduce the clouds of black smoke emitted by many older diesel vehicles.

Use of biodiesel is growing in America, not just in privately-owned vehicles, but also in government and company-operated automobiles. Many government bus fleets and industrial vehicles now use a mix of diesel and biodiesel fuels. Such use complies with Congressional laws that set guidelines for cleaner air and increased use of alternative fuels. Biodiesel is a little more expensive at the gas pump than standard diesel. However, bus fleet owners don't have to purchase any new or specialized equipment to use biodiesel.

The trend toward increased use of biodiesel could be a boon for American soybean farmers, by increasing the value of soybean oil. A study completed in 2001 by the U.S. Department of Agriculture stated that biodiesel could increase the value of soybeans by an average of 17 cents annually through 2010. The study estimates that could result in a $5.2 billion boost to the U.S. farm economy over 10 years.

But as the Energy Department's John Farrel points out, the biofuel isn't derived exclusively from agricultural products. He says that the Fats and Proteins Research Foundation is looking into alternative sources for biodiesel. "They're talking about french-fry grease, [restaurant-derived] yellow grease. We've done demonstrations with yellow grease," he says. "The fuel itself, it's a little bit different. It's also a viable alternative source. Obviously, in urban areas where you have a lot of fast-food chains and things like that, there is a problem with yellow grease disposal. There are some opportunities there."

One enterprising individual is pursuing some of those opportunities with a business that recycles restaurant grease and used vegetable oil into an auto fuel. Justin Carvin is the founder and owner of Greasecar Vegetable Fuel Systems. He markets several different kits designed to allow a standard diesel engine to burn vegetable oil in addition to diesel fuel. The system adds a second fuel tank to accommodate restaurant grease, and a series of filters that prevent impurities in the grease from fouling the engine.

Mr. Carvin says that so far, the conversion kit has worked on every diesel car he's tested. "They all react positively, some better than others. The brand-new Volkswagen engines, because it's a much more controlled injection, and because those sensors do compensate for viscosity issues, they run much better," he says. "The more refined the engine, the better it's going to perform with varieties of different fuel characteristics, but we haven't found a diesel engine that we haven't been able to convert and run successfully with this, at least as well as they run on diesel fuel."

While Mr. Carver is currently focusing on marketing the conversion kits in North America, he admits that his conversion kit might sell better in Europe. "Those countries have a more open mind about fuel, and diesel vehicles are much more common, as well as fuel costs are a lot higher," he says. "So the incentives are much greater to use a product like this. Our long-term goal is really putting this in place in other countries, especially developing countries, that could really utilize this."

Experts caution that people should be careful about putting non-approved fuels in their cars. But John Farrel believes it is essential for the United States and the world to continue to find and use new, renewable sources of fuel. "Energy Diversity is going to be an issue. I don't see us totally getting away and using just biodiesel, just ethanol," he says. "There are limits there. But I think it's needed in the near-term as an insurance policy to help control the prices in the world market. You know even if we're talking 20 percent of the mix, 20 percent on the spot market, would make a big difference in terms of the overall costs of petroleum based fuels."

Mr. Farrell adds that even if America could reduce its foreign oil dependence by twenty percent, it would help the country save a significant amount of money long-term. And like growing numbers of energy experts, he believes alternative fuels like biodiesel will be a key to making this a reality.