Speed of sound measurements were carried out in liquid tridecylbenzene and pentadecylbenzene at pressures from atmospheric up to 150 MPa in the temperature range from (293 to 383) K using a pulse technique operating at 3 MHz. Additional density measurements were performed up to 60 MPa. From these measurements, the density was evaluated up to 150 Mpa and the isentropic compressibility was determined in the same P-T domain.