Gas-liquid mass transfer behavior in a bubble column is investigated. The used reactor is of 6 m height and has an internal diameter of 0.15 m. The classical 'gassing out' dynamic method is used to obtain the dissolved oxygen (DO) concentration profiles. An analytical description of the dissolved oxygen concentration evolution with time following the switch in the inlet gas is presented and allows the evaluation of the gas-liquid volumetric mass transfer coefficient for the different superficial gas velocities used. The comparison between the k(L)a values determined from this exact solution and those obtained in the same reactor from a more complete and sophisticated model, numerically solved, shows a good agreement. (C) 2006 Elsevier B.V. All rights reserved.