Flow regimes in gas-liquid-solid fluidized beds encountered at different operating conditions, column diameters and particle sizes are classified using a statistical method [Diks, C., van Zwet, W.R., Takens, F., DeGoedc, J., 1996. Detecting differences between delay vector distributions. Physical Review E 53, 2169-2176] that allows comparison of the attractors characterizing their dynamics. Time series of the single solid tracer particle positions, obtained by the computed automated radioactive particle tracking (CARPT) technique, are used to reconstruct the attractors for each examined operating condition. The test constitutes a reliable way of objectively diagnosing the flow regime in a three-phase fluidized bed since experiments within the same flow regime have similar dynamical characteristics, while there is a huge hydrodynamic change between experiments carried out in different flow regimes. (c) 2007 Elsevier Ltd. All rights reserved.