Oil refineries are industrial process plants where crude oil is transformed and refined into more useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel, and fuel oils.

Caustic Soda is used in oil refineries to remove impurities such as mercaptans and other sulfur compounds from petroleum products in order to meet regulatory specifications. This process is referred to as a “caustic wash”.