In an oil refinery crude oil is desalted to remove inorganic salt like sodium chloride, an ionic compound responsible for the salinity of seawater.
An oil refinery or petroleum refinery is an industrial process plant 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. It is then desalted to remove inorganic salts (primarily sodium chloride). Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. 
