The hydrodynamics of fluidized beds of FCC particles in a column of diameter 0.29 m were investigated based on gauge and differential pressure signals, as well as optical voidage probe data for conditions approaching and beyond the onset of the turbulent fluidization flow regime. It is shown that any treatment of the system as a dense phase/dilute phase binary is oversimplified given the broad spectrum of properties and the lack of clear delineation between two separate phases. On the other hand, chaos analysis indicates complex bifractal behaviour, with two separate values of the Hurst exponent corresponding to different scales of motion, while wavelet analysis is successful in again decomposing signals into scales of motion associated with voids and separate particles. (C) 2003 Elsevier B.V. All rights reserved.