The effects of different methods for elevating the OTR (oxygen transfer rate) during foreign gene expression and the cell growth of recombinant Escherichia coli BL21 were investigated. Two strategies were introduced to control DO (dissolved oxygen) levels in the fermentation broth: (i) increasing fermentor pressure and (ii) supplying oxygen-enriched air. These two methods were compared with the glucose feedback model, which acted as the control. By adopting a fed-batch method of cultivation, the cell yield coefficient (YX/S), accumulation of acetic acid and volumetric product yield (Yp) were measured or estimated. Adoption of these two methods led to an improvement in the OTR. The cell density and volumetric product yield in the cultivation controlled by increasing the fermentor pressure reached 77 g x l(-1) (dry cell weight) and 14 g x l(-1) respectively, which were much higher than those obtained with the strategy of supplying oxygen-enriched air (48 and 6 g x l(-1) respectively) and in the control (46 and 7 g x l(-1) respectively). The results indicate that increasing fermentor pressure is an effective way to enhance the OTR and recombinant protein (human-like collagen) productivity.