To improve xylanase productivity from Penicillium canescens 10-10c culture, an optimization of oxygen supply is required. Because the strain is sensitive to shear forces, leading to lower xylanase productivity as to morphological alteration, vigorous mixing is not desired. The influence of turbine design, agitation speed, and air flow rate on K(1)a (global mass transfer coefficient, h(-1)) and enzyme production is discussed. K(1)a values increased with agitation speed and air flow rate, whatever the impeller, in our assay conditions. Agitation had more influence on K(1)a values than air flow, when a disk-mounted blade＇s impeller (DT) is used; an opposite result was obtained with a hub-mounted pitched blade＇s impeller (PBT). Xylanase production appeared as a function of specific power (W/m(3)), and an optimum was found in 20 and 100 L STRs fitted with DT impellers. On the other hand, the use of a hub-mounted pitched blade impeller (PBT8), instead of a disk-mounted blade impeller (DT4), reduced the lag time of hemicellulase production and increased xylanase productivity 1.3-fold.