Crude oil is a liquid that comes from reservoirs below the earth's surface.
Natural gas is a gas or vapor that is also stored in reservoirs below the ground.
Crude oil and natural gas are often referred to as petroleum . Crude oil and natural gas are composed of molecules containing carbon and hydrogen atoms. Hydrogen is most commonly found in water which is composed of two hydrogen atoms and one oxygen atom. The carbon atom, represented by the letter C, is found in the mineral coal or in the carbon dioxide which we exhale when we breathe. Carbon dioxide is composed of two atoms of oxygen and one atom of carbon.