The generation of acidic waters and the release of dissolved metals from inactive sulphide mine-tailings disposal is a well-known environmental problem. The flux of oxygen across the surface of the tailings was determined under different physically-controlled environmental conditions and related to the oxidation rate of pyrrhotite mine-tailings. This work was conducted to verify: 1) the consistency in oxygen flux rate measurements in the field within small areas and, 2) the importance of moist layers near the ground surface in the control of the oxygen flux. The flux of oxygen across the surface is related to a relative oxidation rate of the tailings, and it can be concluded from the study that differences in the degree of saturation as a result of fine-grain layers, hardpan formation or a general high water table can control the overall rate of oxygen flux into tailings and reduce the relative rate of tailings oxidation by more than three orders of magnitudes. -from Authors