Low concentration particle transport in multiphase horizontal pipes in the presence of a viscous liquid is experimentally investigated using a 0.05 m diameter pipe. The experiments were conducted for a wide range of liquid and gas flow rates in both intermittent and stratified flow. Critical velocity was defined as “minimum required liquid and gas flow rates to keep particles constantly moving in the pipe”. Critical velocity is defined in a way to make sure all particles are continuously moving along the pipe and as a result prevents forming a stationary bed of sand. The experimental data obtained in the current study shows that the required gas flow rate to meet critical velocity definition increases by decreasing liquid flow rate. Moreover, the effect of physical parameters such as sand concentration, sand size and liquid viscosity is also experimentally investigated. The experimental data obtained in this study shows that critical velocity is a function of sand concentration and sand size and increases by increasing either within the examined range of particle concentration and size. Regarding the effect of carrier liquid viscosity, the experimental data reveals that by increasing viscosity the minimum required flow rates to constantly move sand along the pipe increases.