Abstract Water holdup measurements with conductivity probe were conducted in a 2.54-cm pipe of oil–water flow with and without Drag-Reducing Polymers (DRP) in a horizontal pipe. The water holdup was significantly influenced by the injection of DRP at same inlet flow rates. The water holdup of oil–water with DRP is larger than that without DRP for low superficial water velocities and less for high superficial water velocities. The results showed the possibility of using DRP for separating and changing the distributions of oil–water and droplets mixture. An explanation of the effect of DRP on water holdup as a function of drag reduction and flow pattern changes is presented in this paper.