The lubricating properties of model systems based on overbased calcium sulphonate have been studied by sirnudating various kinematic, temperature, and load-speed conditions of fiiction machines as well as by investigating the physical chemistry of friction surfaces. It is found that overbased sulphonate complex grease shows good antifriction, antiwear, and extreme-pressure properties. A synergistic action of calcium tetraborate with overbased sulphonate has been shown. It is found that calcium 12-hydroxystearate, however, has little effect on lubricating properties, but it improves the thixotropic characteristics of a sys tem .