The hydrodynamics in a riser can be explained in terms of the coexistence of a dense bed, a decaying entrainment and a dilute refluxing transport. The model equations previously developed by Rhodes et al, were tested against experimental data obtained in a 0.1 ID m riser. The predicted axial pressure drop is in agreement with the experimental data provided the entrainment decay constant a is taken equal to approximately 0.4. Experimental data were also used to predict the transport velocity U-TR Equation (1) predicts literature data to within approximately 20%. The ratio of the slip velocity to the particle terminal velocity largely exceeds the value of 1. Using a slip factor, as introduced by Patience et al., enables us to examine the variation of the slip velocity over the height of the riser.