Water-in-oil emulsions formed during oil slicks or petroleum production are known to be stabilized by surfactant molecules that naturally occur in the crude oil, e. g., asphaltenes, which are quite lipophilic in nature. Demulsifier substances combine with naturally occurring surfactants to attain a so-called optimum formulation at which the stability of the emulsion is minimum. The attainment of this formulation is related to the hydrophilicity and concentration of the added demulsifier, and a general phenomenology of the demulsification process is outlined.