The effect of liquid and solid transfer vectors (silicone oil and Desmopan, respectively) on the gaseous interfacial area (a(g)) was evaluated in a two-phase partitioning bioreactor (TPPB) using fresh mineral salt medium and the cultivation broth of a toluene degradation culture (Pseudomonas putida DOT-T1E cultures continuously cultivated with and without silicone oil at low toluene loading rates). Higher values of a(g) were recorded in the presence of both silicone oil and Desmopan compared to the values obtained in the absence of a vector, regardless of the aqueous medium tested (1.6 and 3 times higher, respectively, using fresh mineral salt medium). These improvements in a(g) were well correlated to the oxygen mass transfer enhancements Supported by the vectors (1.3 and 2.5 for liquid and solid vectors. respectively, using fresh medium). In this context, oxygen transfer rates of 2.5 g O-2 L-1 h(-1) and 1.3 g O-2 L-1 h(-1) were recorded in the presence of Desmopan and silicone oil, respectively, which are in agreement with previously reported values in literature. These results suggest that mass transfer enhancements in TPPBs might correspond to an increase in a(g) rather than to the establishment of a high-performance gas/vector/water transfer pathway. (C) 2009 Elsevier B.V. All rights reserved.