The absorption of sound in air at frequencies from 4 to 100 kHz in 1/12 octave intervals, for temperatures from 255.4° K (0° F) to 310.9° K (100° F) in 5.5° K (10° F) intervals, and at 10% relative‐humidity increments between 0% and saturation has been measured. The values of free‐field absorption have been analyzed to determine the relaxation frequency of oxygen for each of the 92 combinations of temperature and relative humidity studied and the results are compared to an empirical expression. The relaxation frequencies of oxygen have been analyzed to determine the microscopic energy‐transfer rates.