The average price of conventional gasoline at the pump is currently between $3.60 and $3.70 a gallon. With persistently increasing prices, alternative fuels are increasing in popularity. Popular alternative fuels can produce the same results as standard gasoline, but at a fraction of the price. Because of the amount of energy needed in a car, the fuel must be in fairly portable form, i.e. a liquid or solid. Internal combustion engines need clean burning fuels in order to maintain optimal efficiency, and the cleanest burning fuels are either gases or liquids. Hence, both conventional fuels and alternative fuels are--almost without exception--liquids. Biofuels are among the foremost of the alternative fuels. Included in this group are options such as biodiesel, green diesel, and vegetable oil. Biodiesel is advantageous because, just as sugar is biodegradable, so is biodiesel. It's one-tenth as lethal as salt, and possesses a very low tendency to combust at typical storage temperatures. Vegetable oil is particularly favorable in older engines. Because of the thickness of the liquid, it must either be heated prior to being combusted or the engine must not have implemented various new designs that require a thinner fuel, such as unit injection electronic diesel injection systems. Alcohol fuels include such compounds as methanol, ethanol, and butanol. Methanol is often times mixed with gasoline, in particular in racing cars in many countries. Ethanol is the type of alcohol found in alcoholic beverages and is, likewise, usually mixed with gasoline prior to use in a car. It's becoming more popular each year, with the amount of ethanol produced for transportation tripling between 2000 and 2007. The United States currently leads the world in ethanol fuel production. Butanol is more similar to gasoline than methanol or ethanol, and brings with it the added benefit of ease of transportation. Because the liquid tolerates water contamination better and is less corrosive, butanol fuel can be safely transported through pipelines rather than by tanker truck. Ammonia can also be used for fuel. By using ammonia, cars can completely eliminate emissions. Ammonia is relatively cheap and is extremely clean when it burns. While many alternative fuels require significant alterations to the car’s engine, ammonia requires only mild modifications to the carburetors and injectors. The downside of using ammonia is that the output of energy is less than when burning conventional gasoline. In a smaller car this likely won't prove to be a huge problem, but in larger vehicles it may prove to be a significant impediment. Hydrogen is often talked about as a viable alternative fuel, and the reason is mainly the cleanliness of its burn. In chemical terms, burning means to add oxygen to a substance. In the case of hydrogen, adding oxygen creates H2O, or water. In addition, concern for spontaneous combustion in a car is at a minimum, bearing roughly the same amount of risk as standard gasoline. For reasons of practicality and needed energy output, hydrogen should be in a liquid state to be used as an efficient alternative fuel. It seems automotive technology is leaping ahead on a regular basis. Soon you may own a vehicle that has never seen a drop of conventional gasoline!