The Sarawak Integrated Gas Network is one of the largest and arguably most complicated offshore gas networks in the world due to its intricate physical layout comprising of more than 20 fields producing with total capacity of more than 4000 MMscf/d, supplying to 3 LNG plants. As there are various operators in the network operating different Production Sharing Contracts (PSCs) and Gas Sales Agreements (GSA), commercial arrangements are essential to govern the production policy of the network to ensure PSC and GSA obligations and/or entitlements are honoured. Gas quality management by blending of gas is another aspect to be considered as each of the 3 LNG plants have constraints on contaminants such as CO2 and H2S and each field has varying contaminant levels. Integrated Production Systems Model (IPSM) is used extensively for the production forecast of integrated gas networks as pressure interaction via surface network between the different wells have a significant impact on the reservoir performance. However, due to the combination of physical and commercial constraints of the Sarawak Gas Network and the additional complexity due to contaminants management, generic IPSM models are unable to accurately handle both physical and commercial requirements. As such, the traditional workflow for Sarawak Gas Network required a workaround where IPSM models are used in combination with post processing spreadsheet to manually tweak production forecasts in order to honour commercial and gas quality constraints. This was cumbersome and also negated the real benefits of IPSM. The recent rebuild of the Sarawak IPSM model with the Shell proprietary tool, "Hydrocarbon Field Planning Tool" (HFPT), addresses this challenge by incorporating the commercial arrangements within the model. This is made possible as HFPT allows for flexible scripting which enables asset specific functionality to be modeled. The approach is essentially a 2 step approach within HFPT, where field capacity is derived based on physical constraints (as per generic IPSM models) and a second step where production nomination is managed with a series of rules designed to mimic operational practices to align production nomination with commercial arrangements and for gas quality management. The Sarawak HFPT model has been used extensively for Business Planning and resource reporting exercises to ensure the production forecasts are robust and credible. With this novel approach, the revamped Sarawak IPSM model is capable of generating production forecasts which integrates both commercial and physical constraints as well as contaminants management without the need to evaluate the commercial arrangements as a post processing step.