BACKGROUND: Methane is an important greenhouse gas and its biological oxidation constitutes a cost-effective alternative for low concentration emissions. Nevertheless, due to its low aqueous solubility (similar to oxygen), gas mass transfer is often the limiting step. Two-phase partition bioreactors (TPPBs), have been proposed to increase the biodegradation of poorly soluble compounds. In this work, the effect of stirring rate and silicone oil fraction on abiotic volumetric oxygen transfer coefficient k(L)a(o2), and methane elimination capacity (EC) by a methanotrophic consortium in a stirred tank was studied. RESULTS: In abiotic conditions, the k(L)a(o2) increased when increasing both factors. Nevertheless, a negative effect on k(L)ao(2) was observed with silicone oil at the highest stirring rate (800 rpm). During methane biodegradation experiments, EC also improved when increasing both factors, but contrary to abiotic k(L)a(o2), it was not affected at the highest stirring rate. While stirring rate was the dominant variable determining methane biodegradation, the effect of oil fraction was only significant above 200 rpm. A maximum EC improvement of 700% was observed when increasing stirring rate from 200 to 800 rpm with 10% of silicone oil. CONCLUSIONS: Increasing both stirring rate and oil fraction enhanced EC. The results were different from those observed with k(L)a(o2), suggesting that k(L)a is not sufficient to describe properly the mass transfer in TPPB because other factors (interfacial contact between the phases and physicochemical properties of organic phase) should be considered. (C) 2010 Society of Chemical Industry