Primary nanoparticles in gas-fluidized beds are agglomerated in multi-stage complex-agglornerates formed by several steps. The size of the complex-agglomerates can be estimated by a simple equation obtained from the balance between the local shear force on the particle attached at the outer layer of the agglomerate and the interparticle adhesion force. Usually the bed of complex-agglomerates can be fluidized homogeneously, with large bed expansion and absence of appreciable gas bubbles. In the nonbubbling regime the expansion of the bed can be described by a modified Richardson-Zaki equation. At high gas flows large bubbles can develop that curtail further bed expansion. Yet in some cases the fluidized bed transits directly to elutriation. We provide a criterion to predict either the onset of gas bubbles or the suppression of bubbles. As the gas flow supply to the fluidized bed is decreased there is a point at which the nanoparticles are jammed in a loose configuration characterized by a particle volume fraction that we relate to the ratio of interparticle adhesion to particle weight. (C) 2007 Elsevier Ltd. All rights reserved.