Propellants are used in the production of pressurized gas or energy. The gas or energy is then used to propel a vehicle, projectile, or other objects. The most common propellant is fuel, whether it be gasoline, jet fuel, rocket fuel, etc. When propellants are decomposed or burned, they release the propellant gas. Some propellants are liquids that can be vaporized. Propellant gas, or exhaust, propels object forward by using a chemical reaction or combustion which increases its pressure.