Abstract: Frictional pressure drops of gas-oil-water flows in a horizontal steel pipe and in a Plexiglas pipe were measured and compared. Superficial velocities ranging from 0.6-2.0 m/s for liquid and from 0.2-2.2 m/s for air were investigated. The tested water fraction in the liquid ranged from 18% to 100%. Experiments expressed, under the same conditions, the three-phase frictional pressure drop gradient of the Plexiglas pipe was greater than that of the steel pipe during small water fraction in liquid. As the water fraction increased, the latter was greater than the former. This expressed, besides pipe wall roughness, the wetta-bility of fluids to pipe materials, the adhesion among them and the water fraction etc. might also be influential factors on the three-phase frictional pressure drop.