This paper describes the coupling of a pipeline network model to a reservoir simulator and its application to optimize the production strategy of two Mobil field developments. Mobil’s PEGASUS simulator is an integrated, all-purpose reservoir simulator that handles black-oil, compositional, faulted, and naturally fractured reservoirs. We have extended the simulator to allow simultaneous modeling of multiple reservoirs coupled with surface pipeline networks and processes. This allows us to account for the effects of geology, well placement, and surface production facilities on well deliverability in a fully integrated fashion. We have also developed a gas-contract allocation system that takes the user-specified constraints, target rates, and swing factors and automatically assigns rates to the individual wells of each reservoir. This algorithm calculates the overall deliverability and automatically reduces the user-specified target rates to meet the deliverability constraints. The algorithm and solution technique are described. This enhanced simulator has been applied to model a Mobil field development in the Southern gas basin offshore the U.K., which consists of three separate gas reservoirs connected by means of a pipeline network. The simulator allowed us to determine accurately the effect of varying the development timing of these reservoirs on individual reservoir and total field performance. Several development scenarios are shown to illustrate the capabilities of PEGASUS. Another application of this technology is in our field developments in North Sumatra, Indonesia. Here the objective is to optimize the development of multiple fields economically to feed the P.T. Arun liquid natural gas (LNG) facility. A range of gas compositions, well productivities, and facilities constraints are considered in an integrated fashion, resulting in improved management of these assets. Model specifics are discussed.