The liquid phase hydrogenation kinetics of five di- and trisubstituted alkylbenzenes, xylenes, mesitylene, and p-cymene were determined in a semibatch reactor operating at hydrogen pressures of 20-40 atm and at temperatures of 95-125 degrees C. Commercial preactivated catalyst particles of nickel-alumina were used in all experiments. The hydrogenation activity of the aromatic compound was affected by both the number of substituents and their relative positions in the benzene ring. The trisubstituted benzene (mesitylene) had a lower reaction rate than the disubstituted compounds (xylenes). The activity of the different substituent positions decreased in the order para > meta > ortho. The main reaction product was always the completely hydrogenated cycloalkane; no cycloalkenes were detected. The hydrogenation rates were virtually constant at low and intermediate conversions of the aromatics, but at high conversions the rates decreased. Rate equations based on the formation of partially hydrogenated surface complexes were derived, and the kinetic parameters were estimated from a heterogeneous reactor model with nonlinear regression analysis. The rate equations were able to describe the features of the experimental data.