Three-phase (G/L/S) horizontal pipe flow data collected from the literature are used to evaluate the performance of a number of correlations designed to predict the pipeline pressure gradient. In the present study, a number of popular two-phase gas-liquid pressure loss correlations were modified for three-phase flow predictions. The primary modification is to assume that the slurry (L/S) mixture behaves as a singlephase. The modified Dukler and the Beggs and Brill correlations did not provide accurate estimates of the three-phase pressure gradients. When the classical Lockhart-Martinelli (L-M) correlation was used, along with a kinematic friction loss model to calculate the slurry (L/S) superficial flow pressure gradient, accurate predictions of the three-phase (G/L/S) pressure gradient were obtained provided the slurry did not exhibit non-Newtonian behaviour and that Coulombic (sliding bed) friction was negligible. Additional experiments should be conducted before the improved version of the L-M correlation is applied to commercial installations with pipe diameters greater than 100mm.