In order to understand the behaviour of two-phase flow in inclined pipes, an extensive programme of work has been undertaken using the Inclinable Facility in the laboratories of the School of Chemical, Environmental and Mining Engineering at the University of Nottingham. The test pipe (6.5 m long) could be positioned at angles between -20° downwards and vertical upwards. Two pipe diameters were used; namely 38 mm and 67 mm. The fluids used were air and water. Superficial velocities for air ranged from 0.15 to 8.9 m/s and from 0.04 m/s to 0.7 m/s for water. Time series of liquid holdup (using capacitance probes) and pressure drop (differential pressure transducer) were measured. In addition, a high speed video system was used in order to obtain image sequence of the flow under different selected conditions. It was found that for upward inclined flow most of the experiments fall within the slug flow regime whereas for inclined downward flow the dominant flow pattern is stratified flow. For horizontal flow, the flow regime depends more on the gas and liquid superficial velocities. Data for liquid holdup, pressure drop, frequency and translational velocity of periodical structures are reported. Comparisons with literature correlations and data are performed as well. Frequency was found to be strongly affected by inclination angle and a correlation has been proposed. An effect of the pipe diameter is also found under certain flow conditions mainly on the liquid holdup, pressure drop and structure velocity. Increase of pipe diameter displaces the bubbly-slug transition to the right hand side on the flow pattern map for inclined flow, and for horizontal pipe the stratified-slug transition is moved up. In addition, a CFD code has been used to successfully model the hydrodynamics of In addition, a CFD code has been used to successfully model the hydrodynamics of the slug flow pattern, using the Volume of Fluid model based on the Euler-Euler approach. The modeling results are validated with the experiments and also provide more detailed information on the flow such as the velocity field.