We present an investment analysis tool for natural gas infrastructure development. The model takes a system perspective and considers all existing infrastructure as well as the potential expansions. We formulate the investment problem as a deterministic mixed-integer linear program. We extend existing infrastructure analysis models within natural gas by adding pressure ﬂow relationships and by modeling the gas quality in the transportation system. In this paper we present the motivation for the model functionality as well as the main components in the model. We also discuss a relevant investment case from the Norwegian Continental Shelf to exemplify typical model sizes as well as solution times.