Simulations with four-way coupling are performed for two-dimensional gas-solid flows in a fluidized bed. The motion of particles is treated by a Lagrangian approach and particles are assumed to interact through binary, instantaneous, non-frontal, inelastic collisions with friction. The model for the interstitial gas phase is based on the Navier-Stokes equations for two-phase flow. The numerical approach has been validated with experimental investigations of the fluctuating motion in a shallow fluidized bed and of cluster characteristics in a fast-fluidized bed. Further on, the influence of the interparticle collision characteristics on the cluster structures and the fluctuating gas-solid motion in diluted flows has been investigated. (C) 2002 Elsevier Science Ltd. All rights reserved.