A resonance tube system has been used to study the propagation of sound in mixtures of gases. The resonance tube consisted of a long duralium tube with a fixed reflector at one end and a plane diaphragm at the other. The diaphragm was vibrated by a moving coil at an amplitude determined by an optical method,and the driving point impedance at a number of frequencies was deduced from the current through the coil. A computer was used to determine the attenuation and velocity from these measurements. Measurements were made in oxygen containing up to 2.6% of hydrogen, helium, carbon dioxide and water vapour, with results which can be described by the equations given in the table below. In addition sound attenuation was measured in the gas filled tube using nitrogen, dry air (free of carbon dioxide) and dry oxygen, and was found to be about 19% higher than that predicted by the Helmholtz Kirchhoff equation.