The economics and physical feasibility of hydraulic fractured completions in the Patchawarra and Tirrawarra tight gas sands of Big Lake Field were evaluated using engineering/geologic design considerations and computer simulation to yield predictions of flow results under a range of treatment volumes. The analysis is based on design studies only, as just one well in the field (Big Lake 4) has so far been hydraulic fracture treated in the subject zone, and to date has not been tested for an extended period. Computer simulation models were generated for five separate layers in the Patchawarra interval and one layer in the Tirrawarra interval. Well performance was evaluated at two locations (Big Lake 1 and Big Lake 3), based on the reservoir layer properties within these wells known from electric logs, limited cores and drill stem tests obtained in four wells on the field. The study results indicate that hydraulically fractured treatments are a practical completion method for significantly increasing flow rates from the zones, but that the completion interval and treatment design will need to be carefully tailored because of the high reservoir temperature (325-360 degrees F.) and the presence of interbedded, low compressive strength coals. The model economic analysis results using a $0.60/MCF gas price indicated a range of optimum treatment volumes from 50,000 to 300,000 gallons. The optimum treatment volume appears to be primarily a function of gas pore volume to be drained, and the well location, with the net enhanced production present value profit being strongly a function of the permeability multiplied by thickness product. The impact of the areal and interval rock characteristics variations on the treatment design and economic outcome are great enough that a field testing programme needs to be undertaken in two or more locations to evaluate the probable economics of the overall field development. Detailed coring and logging during drilling and complete pre- and post-fracture engineering evaluation by pressure transient production testing will be mandatory.