Soil biomass activity may be used as an indicator of pollutant degradation in soil, but methods for estimating soil biomass can be time-consuming. Activity in soil contaminated with oil refinery tar has been assayed using a low flow gas meter to measure oxygen evolved by the decomposition of hydrogen peroxide by catalase in the soil microflora. Each analysis takes 15 minutes. Samples from contaminated land undergoing bioremediation were analysed through a 14 week treatment period and biomass activity compared with pollutant concentrations. An increase in microbial activity corresponded to a decrease in pollutant concentrations.