Liquid fuels are contrasted with solid fuels along with gaseous fuels. Liquid fuels are generally combustible or energy-generating molecules that may be harnessed to build mechanical energy, commonly producing kinetic strength; they also must take the contour of their jar. Most liquid fuels sources in widespread use are produced from fossil fuels; however, there are many types, such since hydrogen fuel, ethanol, along with biodiesel, which are categorized as the liquid fuel.