The kinetics of a gas-liquid reaction, alkene hydroformylation was studied in the presence of a homogeneous catalyst in a pressurised laboratoryscale semibatch reactor. Hydroformylation of propene to isobutyraldehyde and n-butyraldehyde was carried out at 70-115°C and 1-15 bar pressure in 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate solvent with rhodium catalyst using the ligands cyclohexyl diphenylphosphine. In order to evaluate the influence of mass transfer, experiments were made using varied stirring rate from 100 to 1000 rpm at 100°C and 10 MPa syngas pressure. Only at higher stirrings rates, the reaction took place in the kinetic regime. A reactor model was developed comprising both complex kinetics and liquid-phase mass transfer. The model was based on the theory of reactive films. The model is able to predict under which circumstances the hydroformylation process is affected by liquid-phase diffusion of the reactants. Experimental data and model simulations are presented for the hydroformylation of propene in the presence of a homogeneous rhodium catalyst.