The speed of sound in the normal hydrocarbons n-C23H48 and n-C24H50 has been measured up to 150 MPa in the temperature range (293.15 to 373.15) K using a pulse technique operating at 3 MHz. The data have been used to evaluate various thermophysical properties such as density, and isentropic and isothermal compressibilities up to 150 MPa with the help of additional density measurements performed at atmospheric pressure.