Biodiesel refers to a diesel-equivalent, processed fuel derived from biological sources (such as vegetable oils), which can be used in unmodified diesel-engined vehicles. It is thus distinguished from the straight vegetable oils (SVO) or waste vegetable oils (WVO) used as fuels in some modified diesel vehicles.
In this article's context, biodiesel refers to alkyl esters made from the transesterification of vegetable oils or animal fats. Biodiesel is biodegradable and non-toxic, and typically produces about 60% less net carbon dioxide emissions than petroleum-based diesel, as it is itself produced from atmospheric carbon dioxide via photosynthesis in plants. Pure biodiesel is available at many gas stations in Europe.
Some vehicle manufacturers are positive about the use of biodiesel, citing lower engine wear as one of the benefits of this fuel. However, as biodiesel is a better solvent than standard diesel, it 'cleans' the engine, removing deposits in the fuel lines, and this may cause blockages in the fuel injectors.