Sound absorption measurements in pureCO2at atmospheric pressure and 22°C have been conducted which, together with measurements by others, confirm the collision theory of anomalous absorption as developed by Einstein, Kneser, and others. The absorption coefficient is appreciable at frequencies as low as 2000 cycles, and increases to a maximum of 0.317 per wave‐length at 77,000 cycles. This maximum is higher than values obtained by previous workers, and indicates that both the deformation and symmetrical valence vibrations participate in the exchanges between translational and vibrational energy. Small impurities, as water or alcohol vapors, affect the absorption greatly; the entire absorption band is shifted to higher frequencies. Measurements in mixtures ofCO2inO2andCO2inN2indicate that neither theO2norN2is appreciably excited by collisions withCO2. Measurements inCS2reveal an absorption similar to that forCO2except that the absorption begins at about 10,000 cycles. In mixtures ofCS2andO2, the observed absorption at frequencies below 10,000 cycles is accounted for by assuming that only the vibration ofO2molecules is excited by collisions withCS2molecules; at higher frequencies theCS2molecules also are excited, principally by collisions with otherCS2molecules.