Accurate prediction of slug length distribution and the maximum slug length in a hilly terrain pipeline is crucial for designing downstream separation facilities. A hilly terrain pipeline consists of interconnected uphill and downhill pipe sections, where slugs can dissipate in the downhill sections and grow in the uphill sections. Furthermore, new slugs can be generated at the dips (bottom elbows) and dissipate at the top elbows. Although existing steady-state models are capable of predicting the average slug length for pressure drop calculations and pipeline design, they are incapable of predicting detailed flow characteristics such as the maximum slug length expected at the exit of a hilly terrain pipeline. A transient slug tracking model based on a quasi-equilibrium formulation was developed to track the front and back of each individual slug, from which individual slug lengths are calculated. The model was verified with large-scale two-phase flow hilly terrain experimental data acquired at the Tulsa University Fluid Flow Projects (TUFFP). The results show a fairly accurate match between the model predictions and experimental data.