Measurements of speed of sound were carried out in liquid heptadecylbenzene and octadecylbenzene at pressures from atmospheric up to 150 MPa in the temperature range 303 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 and isothermal compressibilities were determined in the same P and T domain. The results were fitted to a Tait-like equation.