A simplified Euler-Euler model was developed for predicting the void fraction and velocity profiles in a vertical upward bubbly, pipe flow. The main objective of this approach is to provide a tool for computing the gravitational pressure gradient associated with a large number of flow conditions. This model is based on existing correlations for the interfacial momentum transfer and turbulence modeling. Assuming a fully developed, axially; symmetric flow, our formulation reduces to a set of first-order equations, which can be solved with relatively fast convergence. The results obtained with our approach are first validated by comparisons with experiments collected in small-diameter tubes taken from the literature. Then, the model results are compared with our experiments at low liquid input, moderate pipe diameter conditions and for various bubble size values. The model is found to correctly predict the evolution of void fraction and velocity profiles associated with bubble size and liquid input changes. The drift-flux model distribution parameter and the superficial gas velocity for various flow conditions was finally computed. The results show a reasonable comparison with experiments. (c) 2005 American Institute of Chemical Engineers.