Natural fuels, or alternative fuels, are any materials and substances that can be made into fuel that are not derived from fossil fuels such as crude oil, coal and natural gas, or from radioactive materials such as uranium, and that are sustainable.
Examples of natural fuels include bio-diesel, bio-alcohol (methanol, ethanol and butane), fuels made from waste materials that releases methane, hydrogen, vegetable oils and propane among others.
The issue with all of these fuels, however, is that the natural fuel technology that is used to produce them still costs more than extracting fossil fuels. Energy technologies determine energy availability, choice of fuels, use efficiency, and the amount of by-product emissions. Research and development is the main way that new technologies become available and more research is required to make natural fuel technologies more efficient and less expensive to produce than fossil fuels.