Crude oil often contains salts that can result in corrosion when processed through a refinery.
Salt in crude oil is typically in the form of salt crystals dissolved in the water that is emulsified in the crude oil. The most common salts are chlorides of sodium, calcium, and magnesium.
Salts are typically removed in a desalting unit before crude is sent to atmospheric distillation. High concentrations of salt in a crude oil grade will affect its market value because of the additional cost of processing it.