Carbon is the main structural element in the hydrocarbon molecules that make up crude oil. Petroleum also contains abundant hydrogen, but carbon atoms form the molecular chains and rings that define its fuels and other products.
Crude oil is a complex mixture rather than a single chemical. Its hydrocarbons include alkanes, cycloalkanes, and aromatic compounds, with molecules ranging from relatively small compounds to very large structures. Refining separates and transforms these molecules into products such as gasoline, kerosene, diesel, lubricants, and asphalt.
Carbon’s ability to form four chemical bonds allows it to build long chains, branches, and rings. That versatility explains why petroleum contains thousands of different compounds. Small amounts of sulfur, nitrogen, oxygen, metals, and other elements are also present and are removed or reduced during processing.