AbstractThis investigation used the glucose oxidase system to simulate oxygen transfer rate in fermentation broths. It was demonstrated that the fungal preparation contained sufficient lactonase activity so thatD‐glucono‐δ‐lactone did not accumulate and that the rate of production of gluconic acid was proportional to the oxygen uptake rate. Enzyme concentrations of 1.5–2 g/1 were found adequate to determine oxygen absorption rates in shake flasks while maintaining the dissolved oxygen concentration of low levels. The apparent Michaelis constant for oxygen,Km(O2), was found to be 27% saturation with air; this value along with experimentally determined uptake rates could be used to calculate dissolved oxygen concentration in lieu of using a dissolved oxygen probe. Enzyme concentrations of 5 g/l were sufficient to give linear acid production and low dissolved oxygen concentrations in a bench‐scale fermenter with no foaming or enzyme deactivation. The method is considered more valid and easier to employ than previously utilized techniques such as sulfite oxidation. Extension of the system to evaluating aeration effectiveness and scaleup of fermentation equipment is