A low-cost alternative approach to reduce landfill gas (LFG) emissions is to integrate compost into the landfill cover design in order to establish a biocover that is optimized for biological oxidation of methane (CH 4). A laboratory and field investigation was performed to quantify respiration in an experimental compost biocover in terms of oxygen (O 2) consumption and carbon dioxide (CO 2) production and emission rates. O 2 consumption and CO 2 production rates were measured in batch and column experiments containing compost sampled from a landfill biowindow at Fakse landfill in Denmark. Column gas concentration profiles were compared to field measurements. Column studies simulating compost respiration in the biowindow showed average CO 2 production and O 2 consumption rates of 107 ± 14 g m −2 d −1 and 63 ± 12 g m −2 d −1, respectively. Gas profiles from the columns showed elevated CO 2 concentrations throughout the compost layer, and CO 2 concentrations exceeded 20% at a depth of 40 cm below the surface of the biowindow. Overall, the results showed that respiration of compost material placed in biowindows might generate significant CO 2 emissions. In landfill compost covers, methanotrophs carrying out CH 4 oxidation will compete for O 2 with other aerobic microorganisms. If the compost is not mature, a significant portion of the O 2 diffusing into the compost layer will be consumed by non-methanotrophs, thereby limiting CH 4 oxidation. The results of this study however also suggest that the consumption of O 2 in the compost due to aerobic respiration might increase over time as a result of the accumulation of biomass in the compost after prolonged exposure to CH 4.