The flow characteristics of high viscosity oil and gas flow show several significant differences with those of low viscosity liquid. Effects of high viscosity oil on characteristics of oil and gas flow are identified. The present experiments are performed on the flow facility which consists of a test section of 26 mm ID and a 5.5 m long horizontal pipe. A range of liquid viscosity from 1000 cP to 7500 cP is investigated. The superficial oil and gas velocities vary from 0.06 m/s to 0.5 m/s and from 0.3 m/s to 12.0 m/s respectively. The resulting flow patterns are identified by Electrical Capacitance Tomography (ECT) and confirmed by videos recorded during the experiments. The pressure and liquid holdup data are obtained by using pressure transducers and ECT system. The experimental results are compared with existing models and show significant discrepancies between low and high viscosity liquid and gas flows. (c) 2013 Elsevier Ltd. All rights reserved.