An intrusive bioptical probe provides radial profiles of the PDF (probability density function) of the bubble, the cloud, and the emulsion phases behaviors in a fluidized bed of Geldart-A particles. The fluidizing velocity ranges between 0.20 and 0.80 m/s. The bed porosity, the overall averaged bubble chords and velocities are well-predicted by correlations of the literature. The cloud thickness is closely related to the bubble chord. The amount of gas traveling through the bubble phase never exceeds 15-20% of the total gas flow rate. The averaged porosity of the bubble, the cloud and the emulsion phases is of 88-92%, 65-70%, and 50-55%, respectively. The reduced bubble porosity distribution obeys a constant normal law over the fluidizing velocity range. Each distribution of the reduced bubble chord and velocity, and of the reduced cloud thickness obey a constant log normal law over the fluidizing velocity range. (c) 2007 American Institute of Chemical Engineers.