Probabilities of fluidization regimes were determined experimentally using frequency domain analysis of pressure fluctuation data. It was assumed that regime transition does not occur at a distinct gas velocity and fluidization regimes coexist at each gas velocity. Three different flow structures (macro-, meso-, and microstructures) were recognized in a fluidized bed. Macrostructure is represented by bubbles, mesostructures are represented by clusters, and microstructure is represented by particles. These structures are the characteristics of bubbling, turbulent, and fast fluidization regimes. Regime probabilities were determined using power spectrum energies of these structures. Experiments were carried out in a 1 m high and 5 cm inner diameter glass column. Pressure fluctuations were measured using a piezoresistive pressure sensor. Sand particles with various diameters (150, 280, and 490 mu m) and fluid catalytic cracking (FCC) particles (73 mu m) were used as solids. Probabilities of fluidization regimes were calculated at various gas velocities. A new procedure was proposed for evaluating the regime probabilities versus gas velocity. It was shown that the proposed correlation is in good agreement with the experimental data and is noticeably better than the method proposed in the literature.