A semibatch reactor concept was proposed for the determination of the kinetics in complex catalytic liquid and gas-liquid systems with reactions of highly varying rates. The method is based on continuous removal of liquid phase from the reactor, while the catalyst remains inside the reactor. The concept was demonstrated by catalytic hydrogenation of citral on Ni catalyst. The primary product (citronellal) is formed very rapidly, while the secondary (citronellol) and tertiary (3,7-dimethyloctanol) products appear much more slowly. With the proposed semibatch concept, the formation of the ultimate products was considerably accelerated and all of the rate parameters were successfully estimated by nonlinear regression analysis. The proposed approach can be extended to fixed beds with recycling as demonstrated by computer simulations.