The catalytic oxidation of fluorene to 9-fluorenone in a fluidized-bed reactor was investigated by modeling of the reactor and simulation of its performance. The ''Bubble Assemblage Model'' of Kato and Wen, the ''Bubbling Bed Model'' of Kunii and Levenspiel and the ''Countercurrent Backmixing Model'' of Potter were applied. From a comparison of simulation results obtained by the various fluidized-bed models and a fixed-bed model conclusions were drawn about the influence of interphase mass transfer and gas backmixing on the conversion of fluorene and selectivity of 9-fluorenone formation. Furthermore, the dependence of conversion and selectivity on temperature and hydrodynamic conditions was investigated. In particular, the implications of a change of hydrodynamic conditions for scale-up were analysed. The highest yield of 9-fluorenone predicted for a bench-scale fluidized bed amounted to 88% (X(F) = 97%, S(NON) = 91%). This yield was lower than in a fixed-bed reactor (Y(NON) = 92%, X(F) = 99%, S(NON) = 93%). A further drop of the yield was predicted when scaling-up from a bench-scale reactor to a commercial size unit (Y(NON) = 54%, X(F) = 86%, S(NON) = 63%).