Both particle-fluid and particle-particle interactions have profound effects on particle segregation and aggregation phenomena. Numerically, these effects are taken into account through an appropriate drag law formulation that should be accurate enough to predict the overall particulate flow behavior. In this work, several drag law models are used to study their effects on particle segregation in a gas-solid fluidized bed. Compared to Syamlal and Bell model, the non-particle-particle drag model yields a significant particle separation in the axial direction, with the tendency of large particles to settle down in the bottom of the bed while small particles gather in the upper part of the bed. The predicted numerical results agree well with Mathiesen's experimental results. The segregation profiles generated by the ad hoc modified drag model and the binarydisperse Van der Hoef drag model are contradictory. Inverse segregation results from the use of the Van der Hoef drag model, which is similar to the Brazil Nut Effect, and the results show significant discrepancies from Mathiesen's experimental results. (C) 2011 Elsevier B.V. All rights reserved.