34 core plug samples from 6 wells were studied to identify the petrological characteristics of the Tirrawarra Sandstone, particularly its diagenetic history and factors controlling reservoir quality. Such information is necessary for the successful design of well stimulation programmes. Extensive diagenetic changes to the Tirrawarra Sandstone on the fields have eliminated virtually all primary porosity, causing widespread low permeabilities. The creation of limited secondary porosity has restored permeabilities to above 10 md in only a few samples. Stimulation of 2 Fly Lake wells has been carried out with variable results. Fly Lake 1 was acidized using HF/HCl and achieved an oil flow of 390 BOPD. A similar treatment of Fly Lake 5 failed to produce any significant flow. The different response may be due to subtle differences in composition with respect to the content of acid-soluble components in the rock. Hydraulic fracturing appears necessary to achieve satisfactory flows from the Fly Lake-Brolga wells, but although the formation does not seem to be water-sensitive, a fines migration problem can be anticipated.