BACKGROUND: Biosurfactants are microbially derived surface-active and amphipathic molecules produced by various microorganisms. These versatile biomolecules can find potential applications in food, cosmetics, petroleum recovery and biopharmaceutical industries. However, their commercial use is impeded by low yields and productivities in fermentation processes. Thus, an attempt was made to enhance product yield and process productivity by designing a fed-batch mode reactor strategy. RESULTS: Biosurfactant (BS) production by a marine bacterium was performed in batch and fed-batch modes of reactor operation in a 3.7 L fermenter. BS concentration of 4.61 +/- 0.07 g L1 was achieved in batch mode after 22 h with minimum power input of 33.87 x 103 W, resulting in maximum mixing efficiency. The volumetric oxygen flow rate (KLa) of the marine culture was about 0.08 s1. BS production was growth-associated, as evident from fitting growth kinetics data into the Luedeking-Piret model. An unsteady state fed batch (USFB) strategy was employed to enhance BS production. Glucose feeding was done at different flow rates ranging from 3.7 mL min1 (USFB-I) to 10 mL min1 (USFB-II). USFB-I strategy resulted in a maximum biosurfactant yield of 6.2 g l1 with an increment of 35% of batch data. The kinetic parameters of USFB-I were better than those from batch and USFB-II. CONCLUSION: Comparative performance evaluation of batch and semi-continuous reactor operations was accomplished. USFB-I operation improved biosurfactant production by about 35% over batch mode. USFB-I strategy was more kinetically favorable than batch and USFB-II. (c) 2012 Society of Chemical Industry