The speed of sound is reported for liquid metals(mercury,indium,bismuth,sodium, and tin) as a function of pressure (0 to 150 atm) and temperature (up to 100°K above the melting point). The result and data are used to obtain expressions for the derivatives of the sound speed with respect to temperature and pressure. These coefficients are then used to determine the parameter of nonlinearity in terms of the ratio B/A of the first two coefficients of the adiabatic expansion of pressure in terms of the density.