Velocity of sound was measured to an accuracy of 0.1% in liquid argon, krypton, and xenon under saturated vapor conditions by a resonance ultrasonic technique. Measurements in argon and krypton were from their normal boiling points to close to their critical points, while those in xenon were from its triple point to close to its critical point. Adiabatic compressibilities of these liquids were calculated in the temperature regions for which density data were available.Analysis of the results indicates that such velocity data can provide a precise test of the principle of corresponding states, in its classical and quantum forms. The corresponding states principle holds quite well in the above liquids when subjected to this test.The velocity data in all cases agree more closely with tunnel model calculations than with cell model calculations.