Emulsions are colloidal dispersions, droplets of one phase dispersed in a second phase.1-3 Crude oil is almost always produced as a water-in-oil emulsion, that is, water droplets stabilized in a continuous crude oil phase (Figure 11.1). Freeproduced water may also be present depending on the water cut. The water and dissolved salts in the emulsion must be separated out before the oil is acceptable for further transportation or treatment at a refinery. This process is called “demulsification” or “dehydration.” In refineries, the process of removing salty washwater from crude is called desalting. The sales specification for crude oil gives a maximum value for both water and solids in the form of a bottom solids and water value. Typically, the desired maximum water content will be in the range of 0.2-0.5%, and the acceptable maximum salt content will be 10-25 lb/1,000 bbl, although the refinery may set tighter specifications for water and salt than this.