Petroleum is a naturally occurring, yellow-to-black liquid found in geological formations beneath the Earth's surface. It is commonly refined into various types of fuels. CRUDE is a form of petroleum that has not been processed and is in its natural state. GAS is a form of petroleum that has been processed to be used as FUEL for heating and cooking. FUEL is a form of petroleum that has been processed to be used as FUEL for vehicles. OIL is a form of petroleum that has been processed to be used as lubricants and other products. GASOLINE is a form of petroleum that has been processed to be used as FUEL for vehicles. Naphtha is a form of petroleum that has been processed to be used as a solvent and FUEL. Blackgold is a slang term for petroleum.