Methane concentration in the explosive range is of particular concern in the confined space of underground mining environments, where the hazards of accidental ignition of methane may be further compounded by coal dust explosions. The aim of this study was to determine whether composted pine bark, could be used as biofiltration support media for methane oxidation and to determine the degradation rates of methane concentrations approaching the explosive range (i.e. 5.5% v/v methane). Although of organic origin, composted pine bark is mainly composed of non-labile and recalcitrant large molecular weight molecules due to the fact that the labile organic compounds in the bark are oxidised during the composting process. Methane removal efficiencies in a composted pine bark biofilter were determined at methane concentrations ranging from 0.1 to 2.5% (v/v) and retention times of 20-400 min. Methane removal efficiencies exceeding 70% were obtained when the biofilter was subjected to gas retention times in excess of 30 min and methane concentrations up to 0.5% (v/v). The data obtained were used to develop an empirical model that successfully described the overall removal efficiency with an R-2 value of 0.97. It was concluded that composted pine bark could indeed be successfully utilised in passive gas-flow biofiltration for the attenuation of methane in worked underground coal mining chambers. (C) 2003 Elsevier Science Ltd. All rights reserved.