Two phase flow in a hilly terrain pipeline, composed of uphill and downhill sections, exhibits a complex transient behavior at low flow rates owing to the accumulation of liquid in the low elbows and gas in the top elbows. At low flow rates gravity has a dominant effect, while frictional losses can be neglected. In this work a simplified modeling approach is proposed that is able to predict the transient behavior of gas and liquid flowing in a complex terrain pipeline with multiple valleys. The condition that marks the boundary between severe slugging cyclic behavior and steady state flow is included. An experimental system which consists of three hilly sections was constructed. The experimental data were compared to the predicted results, yielding reasonable agreement in spite of the simplifying model assumptions. (C) 2016 Elsevier Ltd. All rights reserved.