Biofuels are sources of bioenergy.
Liquid fuels can be synthesized from solid biomass using a gasifier which uses oxygen to produce gas. The removal of the CO2 results in synthesis gas (known as syngas). This process can be used to produce both heating and vehicle fuels.
Ethanol can be be produced from the fermentation of crops such as sugar cane and sorghum. These crops are grown specifically to produce vehicle fuel. Many vehicles in Brazil run on gasohol which has a 26% ethanol content. The use of this fuel cut annual greenhouse gas emissions by 13Mt of carbon (1999).
Bio-ethanol was produced from maize in the USA before the demand for the product collapsed when petrol became the dominant product in the market place!
Vegetable oils can be burned directly in diesel engines but it is better to convert the vegetable oils to biodiesel first. The conversion process requires methanol to be added to the vegetable oil, a process known as transesterification.
In France diesel motor fuel contains 5% of rape methyl ester (RME) which is produced from rape oil. The USA adds oil from soya beans and recycled cooking oil.
Those countries with significantly warmer climates can use up to 30% of vegetable oil in their diesel fuel without transesterification.