In this paper we stress analogies in the hydrodynamic behaviour of gas-solid fluidized beds, gas-liquid bubble columns and bubble column slurry reactors and suggest a unified approach to scale up of these ’fluidized’ multiphase reactors. Using published experimental data it is demonstrated that the analogous hydrodynamic behaviour is not just qualitative but quantitative in nature. It is argued that, because of cross-fertilization of concepts and information, appreciation of analogies can be an invaluable tool in scaling up.