Experiments were conducted to study the hydrodynamic characteristics of a gas-liquid-solid fluidized bed containing commercial hydrotreating catalyst extrudates with both water and oil distillates as the liquid phase. The minimum fluidization velocity and bed expansion data were contrasted with predictions from empirical correlations reported in the literature. Empirical correlations tend to yield relatively smaller errors in reproducing the systems with water than with the organic liquids. Bed expansion predictions for the petroleum distillates systems were substantially improved when the sphericity factor of the extrudates was incorporated to the Begovich-Watson equation.