Biofuel research. Bottles of various products in the stages used to produce biodiesel from a plant oil. The initial oil is extracted from the seeds of the Jatropha curcas plant. The bottle at left is the crude product after solids (dark brown) have been allowed to settle. The bottle at centre contains the product of a later, alkali-refining stage. This is then processed to produce the final product of biodiesel (right). This is suitable for use in a conventional diesel engine. Biofuels such as biodiesel are clean, renewable sources of energy, and have less impact on the environment than fossil fuels such as diesel, petrol and coal.