A discussion is provided of the difficulties and limitations involved in the application of the one-dimensional two-phase flow model to estimate pressure gradients associated with the transport of particles. Two particular cases are investigated, namely, hydraulic conveying and pneumatic transport. The validity of the model is checked by comparing experimental data with predicted values of pressure gradients and Void fractions. New approaches for estimating the interaction forces in hydraulic and pneumatic transport are proposed. It is demonstrated that, despite its Limitations, the two-phase flow model may provide good predictions for the pressure gradients.