Abstract: The characteristics of the miscible process of micelles with oil and water and its effect on the displacement efficiency of slugs are discussed, on the basis of changes in phase volume and phase behavior observed in the selfmiscible process of 150 different sample micelles with oil and water. The miscible process of micelles with oil and water may be considered as a process of self-diffusion process of dilatating micelles and described with Faik's Second Law. The rate of miscibility of micelles with oil increases and of micelles with water decreases with the increasing salt content of water,But, the presence of salt of any amounts in water may cause both dilution emulsification and extractive emulsification in the miscible process of micelles with oil and water. Micelles may thus be classified into 4 types. Results from displacement experiment have indicated that different types of micelles have different displacement efficiency. This should be taken into account when a micelle slug is selected. Generally, the displacement efficiency of type Ⅰ slug is the highest. But, in case of a high surfactant content in type Ⅰ slug, even better results can be expected by using the combination micelle slug of types Ⅲ→Ⅱ.