An experimental investigation of the horizontal transport of solid particles by viscous Newtonian fluids has been conducted. The independent variables were: fluid density, fluid viscosity, particle diameter, pipe diameter, in situ solids concentration and bulk velocity. The measured variables included pressure gradients, delivered solids concentrations, concentration distributions and fluid velocity distributions. The pressure gradient, velocity distribution and delivered solids concentrations could be explained in terms of the slurry viscosity and the local solids concentration, which varied considerably in the vertical direction. This variation of solids concentration is interpreted in terms of particle-particle interactions which oppose the effect of gravity. The experimental results show that pressure gradients of the order of 2 kPa/m are required to transport significant quantities of sand in laminar flow. The experimental results should find application in horizontal oil well technology.