The diagenetic controls on reservoir quality of Middle Triassic reservoir facies are addressed in this paper because their importance is paramount to the understanding of reservoir performance. In this study, reservoir quality is compared and contrasted for two reservoir lithofacies and the implications of porosity structure on efficiency of primary and secondary hydrocarbon recovery is assessed. Middle Triassic reservoir facies of the Peejay Field are confined to the youngest of four parasequences. This parasequence is a prograding shoreface succession containing tidal-inlet deposits. Tidal-inlet fills form the main reservoir facies and are composed of sublitharenites (lithofacies Fl) and bioclastic grainstones (lithofacies G). Tidal-inlet sand bodies are 4-6 km long, 500 metres wide, up to 11 metres thick, and are oriented parallel to the paleoshoreline. Vertical profiles of reservoir quality (permeability and porosity) decrease upward, with variance of values being less for the sublitharenites than for bioclastic grainstones. Sedimentary structures, sediment texture, pore type, size and degree of connectivity control reservoir quality and production. The main porosity type of the sublitharenites is secondary intergranular and characterized by homogeneously connected pores, wide pore-throats and low aspect ratios. In comparison, effective biomoldic porosity of bioclastic grainstones is dependent on the degree of intercrystalline porosity development in matrix dolomites. The high porosity and low permeability values of the bioclastic grainstones may lead to the inefficient flushing of hydrocarbons during waterflooding.