Sound‐absorption and ‐dispersion measurements have been made using the tube method onCO2‐H2Omixtures over the temperature range of 23°–195°C. A single relaxation time was found to describe adequately both the absorption and dispersion curves. The reciprocal of the relaxation time at each temperature was found to be linearly dependent on the concentration ofH2O. The relaxation time τABwas calculated at each temperature, and τABwas found to increase as the temperature increased. A significant result is that log τABexhibited no minimum value when plotted versusT−13, as has been previously reported by Eucken and Numann, but rather log τABshows a linear decrease versusT−13. The number of collisionsZ10(AB) necessary to deexcite the lowest vibrational mode ofCO2has been calculated from the measured relaxation time and is essentially temperature‐independent. [This work was supported by the U. S. Office of Naval Research.]