The speed of sound u in gaseous argon has been measured along 21 isotherms at temperatures T between 110 K and 450 K. At T greater than or equal to 150 K, the greatest pressure on each isotherm was the lesser of 19 MPa and the pressure at which the estimated density was half its critical value. Below T = 150 K, the greatest pressure on each isotherm was limited to that at which the estimated density was about 0.8 of the saturated-vapour density. The measurements were made using a spherical acoustic resonator and have an estimated accuracy which varies from 1 . 10(-5). u at low pressures to 7 . 10(-5). u at the greatest pressure on the isotherm closest to the critical temperature. Second, third, and fourth acoustic virial coefficients have been obtained from the results.