The kinetic characterization of microorganisms degrading volatile organic compounds (VOCs) is difficult due to the low substrate concentration prevailing in these processes. In this work, a simple, accurate and easy-to-implement methodology was proposed to perform the kinetic characterization of VOC-degrading microorganisms. The methodology was applied to Rhodococcus erythropolis using toluene as a model VOC. Besides the assessment of traditional kinetic parameters such as the maximum specific growth rate (mu(max)), substrate half-saturation (K-s) and substrate inhibition (K-1), the methodology here proposed yielded the 46 kinetic parameter, which indicates the relative relevance of the biomass growth rate and bacterial density on the VOC mineralization performance. R. erythropolis exhibited K-s, K-1 and mu(max) values of 0.39 g m(-3), 54 g m(-3) and 0.21 h(-1), respectively. The potential of this microorganism (supporting extremely low K-s and high K-1 values) for boosting the performance of bioreactors treating low toluene concentrations was highlighted. Furthermore, alpha/beta ratios of similar to 50 to similar to 500 were recorded at initial toluene gas concentrations of 1.5-5.2 g m(-3), respectively. These alpha/beta ratios indicated that toluene mineralization under the working conditions was mainly related to the biomass growth rather than to the biomass concentration. (C) 2014 Elsevier B.V. All rights reserved.