Oxygen has long been recognized as a control on the acid-generating reactions which produce acid mine drainage, and great effort has been made to reduce oxygen recharge to mine spoil. To investigate O2availability and the role of thermal convection in O2transport in mine spoil, spoil temperature, O2, and CO2concentrations of spoil gas were measured monthly throughout the entire thickness of mine spoil for 1 year at an abandoned strip mine in Clearfield County, Pennsylvania. O2concentrations deep inside mine spoil were found to be 18% or higher, despite active pyrite oxidation. The O2inside this mine spoil had not been lowered to a level that limited the generation of acid mine drainage. Temperature surveys showed thermal anomalies, which appear to result from heat generated by pyrite oxidation reactions. The field data and a simple model show that thermally induced air convection can be a dominant process maintaining high O2concentration in deep mine spoil.