Microbial oxidation of glucose to free gluconic acid by Gluconobacter oxydans batch cultures was studied with a special reference to substrate and product inhibition. Process kinetics were evaluated by comparing different inhibition models. Substrate inhibition can be best described by the equation of Tseng and Wayman predicting linear inhibition of growth above a characteristic threshold glucose concentration. Non-linear inhibition kinetics was observed, however, for product inhibition and the model of Levenspiel was found to fit the experimental data. The biokinetic model parameters, productivities and conversion degrees on media with different glucose and gluconic acid concentrations were calculated and compared regarding the principal limits of process efficiency. Probable mechanisms of inhibition and possible techniques for their minimization are also discussed.