Crude oil

Petroleum, also known as crude oil and oil, is a naturally occurring, yellowish-black liquid found in geological formations beneath the Earth’s surface. It is commonly refined into various types of fuels. Petroleum consists basically of compounds of only two elements, carbon and hydrogen. Because these elements combine in a large variety of complex ways, however, crude oils vary greatly in their chemical composition. Their physical properties such as color, specific gravity, and viscosity also vary widely.