The surface tension of liquid mixtures is an important physical property in heat and mass transfer at an interface. A differential maximum bubble pressure tensiometer is described. Evaluation of the apparatus with standard chemicals had shown that the apparatus is convenient and reliable. The surface tensions of o-xylene +acetic acid and m-xylene + acetic acid were measured from 303.15 K to 343.15 K over the entire range of concentration. The data were correlated as a function of temperature and mole fraction. The average deviation is less than 1 %.