Crude oil is a dark yellow-to-black oily liquid that is usually found in natural underground reservoirs.
It is formed by hydrocarbons (a hydrocarbon is a compound made up of carbon and hydrogen) with the addition of certain other substances, primarily sulphur.
Most of the crude oil is used to obtain motor gasoline, diesel, heating oil, jet fuel, and liquefied petroleum gases. Thus the crude oil is mostly used to produce energy. Small portion of crude oil is converted into petrochemical feedstock used in production of plastics, rubber, fertilizers, cosmetics and the like.