A method was developed to characterize the kinetics of biodegradation of low water soluble gaseous compounds in batch experiments. The degradation of ethene by resting Mycobacterium E3 cells was used as a model system. The batch degradation data were recorded as the progress curve (i.e., the time course of the ethene concentration in the headspace of the batch vessel). The recorded progress curves, however, suffered gas:liquid mass transfer limitation. A new multiresponse fitting method had to be developed to allow unequivocal identification of both the affinity coefficient, K-aff, and the gas:liquid mass transfer coefficient, Kja, in the batch vessel from the mass transfer limited data. Simulation showed that the K-aff estimate obtained is influenced by the dimensionless (volumetric basis) ethene gas:liquid partitioning coefficient (H). In the fitting procedure, Monod, Teissier, and Blackman biokinetics were evaluated for characterization of the ethene biodegradation process. The fits obtained reflected the superiority of the Blackman biokinetic function. Overall, it appears that resting Mycobacterium E3 cells metabolizing ethene at 24 degrees/C have, using Blackman biokinetics, a maximum specific degradation rate, V-max, of 10.2 nmol C2H4 mg(-1) CDW min(-1), and an affinity coefficient, K-aff.gr expressed in equilibrium gas concentration units, of 61.9 ppm, when H is assumed equal to 8.309.