…they're also facing a decline in popularity because of concerns about adverse effects on air pollution and global warming. Environmental scientists are investing time and money into biofuel as sources of alternative energy suitable for replacing the more traditional fossil fuels.

A biofuel (sometimes spelled bio fuel) is defined as any usable fuel derived from at least an 80% renewable resource. Biofuels are usually made by either processing the living organism itself (see the production of ethanol below) or are a product of an organism's metabolic waste. For example, bioengineers are attempting to harness the hydrogen gas created by algae and bacteria to charge fuel cells for hydrogen powered vehicles.

The most common biofuel, ethanol, is usually derived from one of two sources: corn or municipal waste. Of the two, corn is considered to be less efficient, as it takes a considerable amount of resources to grow. It also affects a country's food supply and therefore may have some bearing on the price a consumer pays in the grocery store. Ethanol derived from municipal waste costs a lot more up front, as communities have to create waste disposal plants specially designed to convert trash to biofuel. Once the ethanol is produced, though, it can be used to power cars equipped to burn E85, a 15% gasoline/85% ethanol mix demonstrated to produce much cleaner emissions than standard gasoline mixtures.