There is a lot of talk these days about "alternative fuels." But just what are these alternative fuels, and why is everyone so excited about them?In the simplest terms, an alternative fuel is any fuel other than gasoline or diesel. Since many alternative fuels are also renewable — and can be produced here in the U.S. — they could reduce our dependence on foreign oil.

Alternative fuels such as biodiesel, ethanol and methanol, have been produced and used on a small scale for decades. They are now being rediscovered due to the rising cost of oil and the instability of world politics. Here's where our oil is imported from — it may surprise you to read who the top supplier is.

Before we get to the specifics, let's clear up a related point. There is a big difference between "energy" and "fuel," even though the terms are used interchangeably. While it is often said that we are in an "energy crisis," this isn't accurate. Energy exists all around us in many different forms. The problem is that energy needs to be stored and transported as fuel. So, technically speaking, we should talk about a "fuel shortage," not an "energy crisis."

To help you better understand this developing area of technology, we've put together a list of the most commonly mentioned alternative fuels and given a brief description of each one.

Biodiesel is used to refer to renewable fuels that can be burned in a diesel engine. Biodiesel is most often made from the oil extracted from a variety of plants, such as peanuts or soybeans, although it can also be made from animal fats. Vegetable oil needs treatment before it can be burned in a diesel engine. Biodiesel can be used at 100 percent strength or blended with petroleum-based diesel fuel, and is used in diesel engines without any modification to the engine. It is both non-toxic and biodegradable. It is nearly free of sulfur and carcinogenic benzene — two of the components of petroleum diesel that the Environmental Protection Agency (EPA) and state emissions boards have issued regulations on because of environmental and health concerns. The main drawback to biodiesel is that it is not widely available yet.