A spherical resonator was constructed to measure the resonance frequencies of sound of various gases. The measurement of the resonance curve was automated to take place at intervals of a tenth of the half-width on both sides of the maximum, and was taken forwards and backwards so that any lack of equilibrium could be seen immediately on the screen. The resonator was placed in a thermostatted autoclave. The diameter of the resonator was determined by calibration with argon. In general, 5-10 isotherms were measured between 250 and 350 K and at pressures between 0.025 and 0.5 MPa for various resonance modes. The evaluation of the sound speeds was done in two ways. First, the acoustic virial coefficients were evaluated for each isotherm, and the ideal gas heat capacity and second thermal virial coefficient derived from these isothermal fits. The second way was a simultaneous fit for all points, assuming temperature functions for the acoustic virial coefficients, but calculating the coefficient of the square term in pressure consistently from the thermal virial coefficients. Results are presented for nitrogen, methane, chlorodifluoromethane (R22), ethane and propane.