The scope of this study included the biodegradation performance and the rate of oxygen transfer in a pilot-scale immobilized soil bioreactor system (ISBR) of 10-L working volume. The ISBR was inoculated with an acclimatized population of contaminant degrading micro-organisms. Immobilization of microorganisms on a non-woven polyester textile developed the active biofilm, thereby obtaining biodegradation rates of 81 mg/L(.)h and 40 mg/L(.)h for p-xylene and naphthalene, respectively. Mond kinetic model was found to be suitable to correlate the experimental data obtained during the course of batch and continuous operations. Oxygen uptake and transfer rates were determined during the batch bioegradation process. The dynamic gassing-out method was used to determine the oxygen uptake rate (OUR) and volumetric oxygen mass transfer, K(L)a. The maximum volumetric OUR of 255 mg O-2/L(.)h occured approximately at 720-722 h after inoculation, when the dry weight of biomass concentration was 0.67 g/L.