A computational study of fully-developed gas-particle flow in vertical risers is carried out, using the model of Sinclair and Jackson [1], in order to assess quantitatively the predictive capabilities of the model. Results from comparisons between model predictions and a large body of available experimental data are summarized. In addition, the growing body of data on gas-solid flows is analyzed in a self-consistent manner. Pita and Sundaresan [2] have recently shown that the model was able to reproduce one set of experimental data surprisingly well although the model neglects some important physics relevant to the problem; for example, only elastic particle-particle collisions were considered. In this study, attention is restricted to the same case, and it is found that, in general, the model predictions compare favorably with the experimental data. Predictions from a model which neglects particle-particle interactions are shown, as well as the effect of these interactions on the complex relationship between the operating variables.