The paper presents experimental results concerning mass transfer between the bulk liquid and the packing surface, along with a mathematical description of this phenomenon. Since the verification of the model proposed requires the knowledge of a number of hydrodynamic parameters which are lacking in the literature, the experiments were carried out to determine the values of these parameters. The paper also summarizes the analyses regarding a mathematical criterion that makes it possible to estimate the values of the operating parameters of the reactor at the moment when the hydrodynamic mode changes from the gas continuous to the pulsing flow regime.