[Dr. Scott W. Tinker] There are two main kinds of biofuels. Alcohols, mostly ethanol, the same alcohol found in beer, wine, and even liquor. In fact, it's made in the very same way by fermenting sugar. Then there's biodiesel made from a fairly simple conversion of plant oils like corn, soybean, and even grape seed. Today, biofuels come from the same agricultural system used to grow food. Biofuels can be used in our existing cars and planes, they're mostly carbon neutral since their CO2 emissions may be absorbed by new plans, and they can be grown domestically reducing energy imports. But their biggest challenge is low energy density. In fact, to make a gallon of corn ethanol take 64 years of field corn. That's using more than 50 plants plus the natural gas and diesel fuel required to fertilize, harvest, and process it. Most studies have shown that corn ethanol doesn't provide any more energy than it took to make it. There are crops that do a bit better, like sugarcane, but to improve biofuels in the future like in many energies will require better efficiency; getting more liquid fuel per acre. There are two ways proposed to do that. Growing special algae that produces a lot of oil for biodiesel and growing specialized energy crops that aren't food which produce huge amounts of cellulose, the woody structure of plants, then using a high-tech enzyme process to break down that entire crop into sugars that can be fermented. This could double or even triple yields per acre. These, and other new technologies that turn food and lumber waste into fuel, are not quite commercial and still very expensive, but they may one day make biofuels cheaper than gasoline. Yet, there is still the challenge of energy density. Just the sheer volume of plant material, arable land, and water required.