An investigation on oxygen mass transfer in shake flasks and in a lab-scale bioreactor is reported. An analysis of the main factors influencing oxygen mass transfer in shake flasks has been carried out using full and fractional factorial designs. The factors investigated were : mixing conditions (rpm); temperature (degrees C); weight of closure (g); liquid hold-up (ml); and geometry of shake flasks. The ANOVA (analysis of variance) showed the importance of the investigated factors on the oxygen mass transfer coefficient. An empirical model with dimensionless parameters has been proposed in order to predict the oxygen mass transfer in several experimental conditions. An investigation has also been performed on the oxygen mass transfer in a lab-scale bioreactor, considering stirring, air flow rate and temperature as factors. Parameters of an usual empirical model for oxygen transfer coefficient have been estimated. The relationships proposed have been obtained in a wide range of experimental conditions, and they can be used both to determine if oxygen limiting conditions occur during biological tests in the shake-flask scale or in the lab-scale bioreactor, and in the phase of translation of experimental data to a bigger scale. Using this model the bioleaching of manganiferous minerals by heterotrophic microorganisms is judged to take place just in microaerobic conditions, i.e. in oxygen limiting conditions.