Hydrocarbon, hy droh KAHR buhn, refers to the most important class of organic compounds. Hydrocarbons contain only the elements hydrogen and carbon. They occur in petroleum and natural gas. Commercial petroleum products, such as gasoline, kerosene, airplane fuel, lubricating oils, and paraffin, are mixtures of hydrocarbons. Some hydrocarbons are found in coal tar and coal gas. Many others are synthesized (made artificially) from hydrocarbons found in nature.