The mass transfer in an airlift reactor is modeled using simple elementary models : the liquid flow in the riser and the downcomer is represented as plug flow with axial dispersion, while the gas-liquid separator and the bottom junction are considered as CSTRs for the liquid. The gas flow in the riser is represented as plug flow. The system of differential equations resulting from the mass balances applied to the different sections of the reactor are solved in the real-time domain using a commercial software (MODEST). The model parameters are evaluated by adjusting the variation with time of experimental and simulated oxygen concentration profiles in the reactor after change from deoxygenation to oxygenation of the recirculating liquid (dynamic method), at six different locations in the riser, gas-liquid separator and downcomer. The model is tested using experimental data obtained with advanced measuring techniques in a pilot airlift reactor. The data agree well with some correlations from literature.