Abstract: Interfacial tension is important in various industry processes, particularly in petroleum recovery where low or ultralow interfacial tension between oil and water bring about great benefit. For the measurement of interfacial tension, serveral kinds of method can be used. Those depending on size and shape of liquid drop including se-ssile drop, pendant drop and sprinning drop methods are suitable. Among them, se-ssile drop method has the advantage of simple equipment and procedure. Usually, the radius of drop equator is necessary for sessile drop method. Hence a drop with contice. In systems of low or ultralow interfacial tension, it is seldom to form a contact angle larger than 90°. This had been a restriction for the application of sessile drop method. In this work, procedures for obtaining interfacial tension from size and shape with small contact angle (<90°) was provided. Good precision of this method was shown by applying to typical system (butanol/water). Comparasons of it with other methods have been made.

Key words: Low interfacial tension, Sessile drop method