A generalized slugging-bubbling fluidized bed reactor model is developed which handles seamlessly the transition from bubbling to slugging fluidization, using the concept of probabilistic averaging developed in earlier work. The ratio of the bubble diameter to the column diameter is employed to correlate the probability of each of these fluidization flow regimes. The model gives a good representation of the conversions within the slugging and bubbling regimes, as well as for the transition between these two regimes. (c) 2006 Elsevier Ltd. All rights reserved.