Measurements were made of the velocity of sound in liquid argon in the temperature range 86–146 °K and at pressures up to 65 atm. The velocity versus pressure isotherms are steeper and more curved at the higher temperatures. At any one pressure, the velocity is a smoothly decreasing function of temperature. Analysis of the results using existing density data showed that the specific heat ratio, γ, decreases with pressure and increases with temperature in this range. The coefficient in Rao's relation was found to increase with temperature at constant pressure, while that in the relation due to Carnevale and Litovitz exhibited no definite trend with temperature or pressure.