Biofuel is defined as solid, liquid or gas fuel derived from recently dead biological material and is distinguished from fossil fuels, which are derived from long dead biological material. Theoretically, biofuels can be produced from any (biological) carbon source; although, the most common sources are photosynthetic plants. Various plants and plant-derived materials are used for biofuel manufacturing. Globally, biofuels are most commonly used to power vehicles]], heating homes [[cornstoves and cooking stoves. Biofuel industries are expanding in Europe, Asia and the Americas.

__TOC__ Biofuels offer the possibility of producing energy without a net increase of carbon into the atmosphere. This is because the plants used in the production of the fuel removed from the atmosphere; unlike fossil fuels, which return carbon that was stored beneath the surface for millions of years back into the atmosphere. Therefore, biofuel is, in theory, more carbon neutral and less likely to increase atmospheric concentrations of greenhouse gases. (However, doubts have been raised as to whether this benefit can be achieved in practice, see below). The use of biofuels also reduces dependence on petroleum and enhances energy security.

There are two common strategies of producing biofuels. One is to grow crops high in sugar (sugar cane, sugar beet, and sweet sorghum) or starch (corn/maize), and then use yeast fermentation to produce ethyl alcohol (ethanol). The second is to grow plants that contain high amounts of vegetable oil, such as oil palm, soybean, algae, or jatropha. When these oils are heated, their viscosity is reduced, and they can be burned directly in a diesel engine, or they can be chemically processed to produce fuels such as biodiesel. Wood and its byproducts can also be converted into biofuels such as woodgas, methanol or ethanol fuel. It is also possible to make cellulosic ethanol from non-edible plant parts, but this can be difficult to accomplish economically.

Biofuels are discussed as having significant roles in a variety of international issues, including: mitigation of carbon emissions levels and oil prices, the "food vs fuel" debate, deforestation and soil erosion, impact on water resources, and energy balance and efficiency.

History and policy

Humans have used biomass fuels in the form of solid biofuels for heating and cooking since the discovery of fire. Following the discovery of electricity, it became possible to use biofuels to generate electrical power as well. However, the discovery and use of fossil fuels: coal, gas and oil, have dramatically reduced the amount of biomass fuel used in the developed world for transport, heat and power. However, when large supplies of crude oil were discovered in Pennsylvania and Texas, petroleum based fuels became inexpensive, and soon were widely used. Cars and trucks began using fuels derived from mineral oil/petroleum: gasoline/petrol or diesel.