Fluidization behavior of binary mixtures of solids is addressed. Three binary systems were considered, obtained by mixing monodisperse granular solids of different size and/or density. A segmented fluidization column equipped with multiple pressure transducers was the experimental apparatus. Monitoring of pressure at different locations along the bed and direct characterization of solids contained in each segment were the experimental tools. The binary granular beds were in one of the following states, depending on gas superficial velocity and initial mixture fraction: fixed, bubbly-free fluidization, transient fluidization, and bubbling steady fluidization. Fluidization regimes were mapped in a gas superficial velocity vs. initial mixture fraction phase plane. Axial solids concentration profiles along the bed and solids segregation rates were also assessed for the three systems as a function of the operating conditions of the bed. Differences and similarities between the systems were analyzed and interpreted in the light of the basic segregation patterns. In particular whether a defluidized bottom layer of jetsam-rich solids is formed upon segregation appears to be an important key to the segregation phenomenology. The currently available models for the prediction of solids segregation in fluidized beds prove to be helpful to understand the qualitative features of the phenomenology, but fall short when quantitative prediction of segregation parameters is afforded. (C) 2004 American Institute of Chemical Engineers.