This thesis reports on a study of three hydrocarbon reservoir units (the Mooga, Hutton and Toolachee Formations) in the Strzelecki region to elucidate their diagenetic history, as part of a basin-wide investigation funded by NERDDC, aimed at providing insights into secondary oil migration, basin hydrology, and the local and regional controls on reservoir quality evolution. The project's specific aims were: (a) to evaluate and quantify the cause and effects of subsurface mineral authigenesis on reservoir quality; (b) to study the nature, distribution and controls on porosity, porosity occlusion and porosity generation in a Cooper/Eromanga Basin hydrocarbon field (with emphasis on reservoir units); (c) to develop a model of Cooper/Eromanga Basin diagenesis that may assist in porosity prediction. The study was based on core and cuttings from 25 wells in Strzelecki Field and another 4 wells in the surrounding smaller fields of Marana, Marabooka and Wanara. 500 metres of core were logged and sampled, and 210 thin sections were prepared and described both petrographically and statistically for mineral abundance, textural features and porosity/permeability information. More detailed sample investigations involved the selected use of stable isotope, electron microprobe, X-ray diffraction and scanning electron microscope facilities to categorize the chemistry and origin of the detrital and authigenic rock constituents. Regional porosity distribution was studied using a combination of computer-plotted sonic-derived porosities calculated from digitized gamma/sonic log responses, and available Delhi Petroleum core analyses. Sandstones within the sequence studied have undergone similar post-depositional clastic diagenetic processes, experiencing porosity occlusion by compaction, syntaxial quartz overgrowths and calcite/ankerite/siderite cementation. Two phases of porosity rejuvenation by mineral dissolution have occurred, pre and post carbonate authigenesis. Secondary porosity has been generated by the dissolution of unstable minerals and authigenic carbonate cements. Evidence for widespread secondary porosity generation is provided by numerous petrographic criteria, but linked with this is the observation that authigenic kaolinite and illite aggregates have infilled both primary and secondary pores, reducing permeability.