The liquid fuel is conveniently stored in a tank and can be easily delivered to an engine without needing bulky batteries or inconvenient piles of coal. It also burns completely without leaving ash behind, as coal does. Since the invention of the internal-combustion engine, and later the jet engine, oil products have become the fuels used to power most of the moving vehicles of the world. The continued use of oil is threatened by its finite supply and by its increasing rate of use. Heat is required for cooking, comfort and many industrial processes.
Heat is one of the most common end uses that different energy resources provide.
Electricity, natural gas and oil provide most home and building heat in industrialized countries today. In sunny places, solar power is often used for both home and hot water heating. Industries use electricity, oil or natural gas to provide the huge quantities of heat they need for processing materials or promoting chemical reactions. Depending upon where the industry is located, its main energy supply could be electricity, oil or natural gas. Some industries, such as pulp and paper, burn their own waste products to provide part of the heat they need.