Oil and gas production can be enhanced by fine tuning wells, using enhanced recovery techniques or by identifying and accessing unswept hydrocarbon compartments. The latter of these can add significant value but is difficult to constrain, particularly in complex geological settings with limited production data. Using working examples from the Northern Carnarvon Basin, Australia, a better understanding of the dynamic behavior of four gas fields is constrained by using a holistic approach that integrates production data analysis techniques, three-dimensional seismic data interpretation, detailed reservoir modeling, and fault seal analyses. Four infill well opportunities targeting 500–600 BCF (14–17 Bm3) of unswept gas were identified. In addition, historical infill well locations (preproduction) were reevaluated and shown not to be viable in the context of the current production data. The examples highlight the complexity in constraining the drainage area of wells and how a holistic approach using multidisciplinary data sets and cutting-edge modeling software capability is vital for effective evaluations. A key outcome is the ability to make more informed decisions through a better understanding of risks, uncertainties, and remaining gas volumes. The fit-for-purpose methodology derived from this work will be replicated in other producing oil and gas fields and incorporated into future prospect evaluations.