This paper presents numerical simulations of slug flow in multiphase pipeline systems using a novel simulation tool PeTra. The slug tracking scheme in PeTra is described. A major feature in PeTra is a moving grid together with a fully integrated front tracking scheme. The slug tracking model enables tracking of slug fronts with limited numerical diffusion. PeTra has been implemented in C++ using object-oriented methods resulting in a flexible and dynamic code. The numerical simulations are compared with experimental data and field data.