A hydrocarbon is an organic compound made up entirely of carbon and hydrogen atoms. These molecules are formed when a single covalent bond holds together one or more pairs of carbon and hydrogen atoms, resulting in a wide range of chemical properties depending on the size and structure of the molecule. Hydrocarbons can be found in various forms such as alkanes (saturated), alkenes (unsaturated) and aromatic compounds (ring-shaped). They are commonly used as fuel sources, including gasoline, diesel, heating oil, and natural gas.