The design of wet-gas pipelines and slug catchers requires multiphase flow simulations, both steady-state and transient. However; steady-state simulation is often inadequately conducted and its potential not fully utilized. This paper shows how mechanistic steady-stale simulation models can be used to obtain not only pressure drop, liquid holdup and flow regime, but also to extract important operational information such as pig transit time, pig exit speed, liquid buildup rate behind the pig, and the rime for the pipeline to return to a steady-state after pigging. A well-designed set of steady-state simulations helps to determine pipeline size, slug catcher size, and pigging frequency. It also serves as a starting point for subsequent transient multiphase flow simulations.