The influence of power dissipation and volumetric oxygen transfer coefficient k(L)a on Bacillus subtilis productivity of lipopeptides surfactin and fengycin was studied in shake flasks in view of scaling-up of this fermentation process. The experiments performed with different flask sizes, relative filling volumes, and shaking frequencies confirmed clearly that lipopeptide production changed in function of power dissipation, via interfacial gas-liquid contact surface and oxygen supply. It was demonstrated that k(L)a is the key parameter controlling the productivity and the selectivity of the bioreaction. Varying the oxygen transfer conditions, the synthesis could be oriented to mixed production or to surfactin mono-production. The fraction of surfactin towards total lipopeptides produced and the maximal surfactin production both increased with k(L)a increase (surfactin concentration about 2 g L-1 at k(L)a = 0.04-0.08 s(-1)), while the maximal fengycin production (fengycin concentration about 0.3 g L-1) was obtained at moderate oxygen supply (k(L)a = 0.01 s(-1)). (C) 2012 Elsevier Ltd. All rights reserved.