Abstract: From the detailed investigation on the quantities of surfactants used in the emulsification of the systems oil/water/surfactant, it can be seen that the exceeding amount of surfactant added in the system was not only useless to the emulsification but also harmful to the stability of the emulsion. There was a limit of the quantity of surfactant used in the emulsification. This limit corresponds CMC (CMC_w + CMC_O). CMC is the criterion for the determination of the quantity of surfactant used in the emulsification.

Key words: Toluene, Xylene, Gasoline, Oleic acid, Emulsification, CMC_O, CMC_W, Criterion