In this work a modified two-fluid model was developed based on experimental observations of the interface configuration in stratified liquid-liquid flows. The experimental data were obtained in a horizontal 14 mmID acrylic pipe, for test oil and water superficial velocities ranging from 0.02 m/s to 0.51 m/s and from 0.05 m/s to 0.62 m/s, respectively. Using conductance probes, average interface heights were obtained at the pipe centre and close to the pipe wall, which revealed a concave interface shape in all cases studied. A correlation between the two heights was developed that was used in the two-fluid model. In addition, from the time series of the probe signal at the pipe centre, the average wave amplitude was calculated to be 0.0005 m and was used as an equivalent roughness in the interfacial shear stress model. Both the interface shape and roughness were considered in the two-fluid model together with literature interfacial shear stress correlations. Results showed that the inclusion of both the interface curvature and the equivalent roughness in the two-fluid model improved its predictions of pressure drop and interface height over the range of studied superficial oil and water velocities. Compared to the two-fluid model with other interfacial shear stress correlations, the modified model performed better particularly for predicting pressure drop. (C) 2014 The Authors. Published by Elsevier B.V.