This process is why crude oil is called a fossil fuel. Crude oil is extracted and used to make fuel and other petroleum products. Hydraulic fracturing is one method used to extract oil and natural gas from deep shale formations.Crude oil is a mixture of a wide variety of constituents.It consists primarily of hydrocarbons, which are chemicals composed of hydrogen and carbon. Crude oil also contains hundreds of substances that include benzene, chromium, iron, mercury, nickel, nitrogen, oxygen, sulfur, toluene, and xylene.here are four types of crude oil: Class A: Light, Volatile Oils: These oils are highly fluid and highly toxic to humans and include jet fuel and gasoline. Class B: Non-Sticky Oils: These oils are waxy and less toxic to humans and include diesel fuel and light crude oil.