Densities were measured for liquid mixtures of m-xylene + diphenylmethane and m-cresol + diphenylmethane at temperatures from 333.15 K to 413.15 K and pressures up to 30 MPa. The Tait equation was used to correlate the results. Isothermal compressibilities of the fluids and their mixtures were calculated. The results showed that the excess volumes of m-xylene + diphenylmethane are negative and those of m-cresol + diphenylmethane are positive at the experimental conditions.