Production from the argillaceous Austin Chalk reservoirs from the Gulf of Mexico Basin is predominately from natural fractures, with some production from tight matrix. To understand Austin Chalk matrix reservoir quality, a database containing 1492 porosity and permeability analyses from 21 wells ranging from South Texas to central Louisiana was constructed. The depositional environment of the chalk is interpreted to have been a deeper-water (below storm wave base) setting on a drowned shelf where bottom waters and sediments varied between oxic and anoxic. Five lithofacies were reviewed where the in-place lithofacies are shown to have a strong effect on reservoir quality. Burrowed marly chalk (lithofacies 1) has the best reservoir quality, with a mean porosity of 6.2% and a geometric mean permeability of 351 nd. Burrowed chalky marl to marly chalk (lithofacies 2) has the second-best reservoir quality, with mean porosity being 5.5% and geometric mean permeability being 214 nd. Slightly burrowed laminated marly chalk (lithofacies 3) has a mean porosity of 4.5% and a geometric mean permeability of 101 nd. Well-laminated chalky marl to marly chalk (lithofacies 4) has the poorest reservoir quality, with a mean porosity of 3.5% and geometric mean permeability of 25 nd. Three measurement methods were used to calculate porosity and permeability: (1) routine core plug (RCP) analysis, (2) Gas Research Institute crushed rock (GRI) analysis, and (3) modified gas expansion (MGE) analysis. Comparison among these methods showed that the RCP method provided anomalously high permeabilities and relatively low porosities. The GRI method yielded moderately high permeabilities but expected porosity measurements. The MGE method appears to produce the best results, giving permeabilities measured down to low-single-digit nanodarcy values and the expected range of porosity. The MGE method also displayed the best correlation between porosity and permeability. The concepts from this study can be applied to other chalks worldwide.