Characterizing regime transition in gas-fluidized beds is of fundamental importance for the successful applications of fluidization technology In this study, we show that a state-of-the-art two-fluid model has the ability to correctly predict the transition from packed bed to fully bubbling fluidized beds To this end, we have studied a deep gas fluidized bed, in which the process of transition is shown much more clearly (see Figure 1) compared to relatively shallow fluidized beds. Pat ocularly, we show that in the process of regime transition, the solidlike and fluidlike states can coexist. We conclude this on the basis of visual observation, global bed pressure drop signals. local solid volume fraction signals. cross-sectional averaged axial granular temperature profiles, and radial particle velocity profiles The presence of the coexisting phases can be easily understood nom the fact that the gas phase is compressible