Sensitivity analysis of Wasp model for pressure gradient in solid-liquid slurries was conducted. The experimental work was carried out in 22-mm ID and 45-mm ID pipelines utilizing slurries composed of spherical glass beads having particle size distribution (PSD) following the Rosin-Rammler distribution and mean size of 50 mu m. The spreads of the distribution were 1.7 and 7, corresponding to wide and narrow distributions, respectively. The slurries examined in this study had concentrations ranging from 5% to 25% by volume. Statistical tests for equivalence of means and variances provided some evidence that Wasp model is more accurate in predicting pressure gradients for the slurries of narrower PSD and at higher solid concentrations. Although the model was designed specifically for relatively large pipes, it was found more accurate in predicting pressure gradients in the 22-mm ID pipeline than in the 45-mm pipeline. Experimental results obtained in the same flow loop diameter indicated that the slurry of the narrower distribution produced higher-pressure gradients than those for the slurry of wider distribution. Pressure gradient increased markedly with increasing slurry concentration regardless of the pipe diameter and slurry PSD. However, the pipe diameter was found to have more significant influence on the pressure gradient than the slurry concentration does. (c) 2007 Elsevier B.V. All rights reserved.