Static holdup was investigated experimentally and theoretically in gas - flowing solids - fixed bed bench-scale contactors. Diverse packing elements were used: Raschig rings, ceramic beads, crushed stone and glass beads. Four different flowing solids particles were examined: sand. propant, alumina and glass. A wide range of solid fluxes and gas velocities were used in this study. The experimental results showed a significant influence of the geometry of the packing elements oil static holdup. The physical properties of the flowing solids also influenced static holdup. A moderate influence of solids flux and a minor influence of gas velocity were observed. An empirical correlation for the prediction of static holdup was developed from theoretical and numerical analyses, based on the available experimental data. This simple equation well predicts static holdup and it contains one parameter that has to be measured in the desirable system - dynamic holdup. Alternatively. dynamic holdup can be predicted by previously proposed models. One of those models was integrated into the proposed correlation for static holdup, which gave quite good results. (C) 2008 Elsevier B.V. All rights reserved.