Biodiesel is an alternative fuel, meaning it comes from natural, renewable sources like animal and plant oils. The inventor of diesel -- Rudolph Diesel -- even experimented with peanut oil when he developed the fuel back in the early 20th century. Petroleum distillate for diesel fuel was more plentiful and less expensive to produce than peanut oil, so diesel was born. Today, scientists are learning how to create biodiesel mostly from soybean oil and yellow grease (restaurant cooking oil that's recycled and processed).

Determining the pros and cons of biodiesel often depends on the source of the information. The issue still is hotly debated in the United States. Some advantages of biodiesel are more technical in nature. It can autoignite and has lubricating properties that help keep fuel injectors and some kinds of fuel pumps running. You can, however, use additives instead for less money to achieve the same effects. The U.S. Energy Information Administration says that biodiesel made from yellow grease is probably more cost competitive than that made from soybean oil [source: Radich]. Other pros are that biodiesel emits fewer harmful pollutants than fossil fuels and helps cut down on petroleum use.

Disadvantages to biodiesel include its poor performance at colder temperatures and its negative effects on fuel economy. Surprisingly, biodiesel actually has worse mileage than diesel fuel. According to the National Biodiesel Board, you can run biodiesel in most regular diesel engines with no modifications [source: National Biodiesel Board]. If you have to modify your car's fuel system, though, a certified mechanic can help. Still, there is a cost involved.

In 2010, producers of biodiesel lost a $1 a gallon tax credit and resulted in a 42 percent decrease in production [source: Cardno Entrix]. The credit was reinstated in 2011 and the U.S. Department of Agriculture announced incentives to make affordable feedstock for biofuels available [source: Williams]. One of the problems with determining the value of biofuels is quantifying costs and environmental effects of livestock and farm production of materials needed to produce the various alternative fuels. Another is studying the fuels' effectiveness under real but controlled conditions to make valid comparisons. In the meantime, proponents of biodiesel will continue to push for its continued funding, development and use in automobiles and airplanes.