Residence time distribution experiments were carried out at ambient conditions in pilot scale upflow reactors. Diluted and non-diluted beds of various lengths and diameters were tested. The axial dispersion model was used to describe the liquid phase non-idealities. Results of Peclet number (Pe), liquid holdup and axial dispersion coefficient for various bed lengths and fluid velocities have been collected. The dependency of the non-ideal flow parameters on bed length is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.