Fuels (up) can be defined as substances that are burned to produce energy. Gasses (6 letters) are a type of fuel that is composed of molecules made up of two or more atoms. Gasses are often used in combustion engines, such as those found in cars and airplanes, to generate power. Gasses are also used in heating systems, such as furnaces, to provide warmth. Gasses are also used in industrial processes, such as welding and smelting, to create heat. Gasses are also used in cooking, such as in gas stoves and ovens, to provide heat for food preparation.