Pressure drops were measured during the co‐current flow of a mechanical oil and tap water in 40 mm inner diameter horizontal test section made from organic glass. Measurements is conducted were made for the oil superficial velocity ranges from 0.04 to 1.2 m/s and the water superficial velocity from 0.04 to 2.2 m/s. The volume fraction of water in the oil‐water mixture changes from 0.05 to 0.976. The frictional pressure loss of oil‐water two‐phase flow was also studied experimentally and theoretically. The main finding is the frictional pressure loss of oil‐water two‐phase flow in flow ranges corresponding to flow pattern. Two fluid model was explored to calculate the frictional pressure loss for stratified flow pattern. Homogeneous model was used to predict the fictional pressure loss for oil‐dispersed stratified, oil‐dispersed and oil annular flow regimes. For three‐layer flow regime, a correlation between flow parameters and the two‐phase pressure drop reference to water phase was proposed. The model predictions are in good agreement with experiment data.