In the present work, a mathematical model is presented for simulating fluidized bed reactors with two Zones. Two reactions have been chosen as being representative of the two main uses of this kind of catalytic reactors: propane dehydrogenation and n-butane partial oxidation. The experimental data obtained in a bench scale plant have been simulated using the same fluid-dynamic model for both reactions, based generally on the description of the three-phase model and kinetic models previously developed. By applying those models, most of the trends experimentally checked can be well forecast, gaining a better understanding of the behavior of reactors and reactions. On the other hand, some parameters that could not be determined experimentally, such as the velocity of solid circulation or the oxidation state of the VPO catalyst, turned out to be among the most important reactor-related variables. (c) 2006 American Institute of Chemical Engineers AIChE J, 52: 3911-3923, 2006.