Poly(3-hydroxybutyrate)-P(3HB)-is a natural biodegradable polyester synthesized by several bacteria, produced from renewable resources. The effects of oxygen transfer rate on the intracellular accumulation of P(3HB) was evaluated, aiming at increasing P(3HB) synthesized by Bacillus megaterium DSM 32(T) in bioreactor batch cultures. Bench-scale bioreactor cultivations were performed under different volumetric oxygen mass transfer coefficients, k(L)a, setting stirrer speed on specified values. The results of this work show that oxygen transfer is a key factor on P(3HB) accumulation by B. megaterium, increasing the P(3HB) intracellular mass fraction from 39% to 62% of CDW at k(L)a condition of 0.006 s(-1). (C) 2013 Elsevier Ltd. All rights reserved.