Two-phase oil-water flows in a 10-cm-dia horizontal pipe have been experimentally investigated to study the effect of surfactant on oil-water distributions. Results show that at input water cut of 20 percent and lower the water layer velocity is lower than mixed layer velocity lip to an input mixture velocity of 1.6 m/s. However at input water cut of 40 percent and higher, the water layer velocity is lower than the mixed layer velocity lip to an input mixture velocity of only 0.8 m/s. Oil and water are much easier to be mixed at the medium input water cuts between 40 and 60 pet-cent. The addition of surfactant enhances the degree of mixing of oil-water flow With tin increase of surfactant concentration, the water layer disappears, oil and water start to mix at lower mixture velocity, and the homogeneous flow pattern was observed at much lower input mixture velocity. Also, the mixed layer occupies a much greater fraction of the pipe. These indicate that corrosion could be reduced at lower input superficial mixture velocity with surfactants in oil-water flows.