All known commercial hydrocarbon accumulations in the Perth Basin, Western Australia, occur within the Dandaragan Trough or along its flanks. Land plant-rich source rocks are widely distributed throughout the Permian, Triassic, and Jurassic sections of the basin. Hydrocarbon accumulations are mainly dry gas and gas/condensate, although secondary occurrences of light, waxy oil are also of economic significance. The Lower Jurassic Cattamarra Coal Measures provide both source and reservoir for gas/condensate accumulations in the central Dandaragan Trough (Walyering, Gingin). Gas at Dongara, Mondarra, and Yardarino may have been generated from both the Lower Triassic and Permian, although there is some evidence that the Permian is the principal source. The associated thin oil leg encountered in parts of these fields is attributed to the oil-prone basal Kockatea Shale (Lower Triassic). Regional studies indicate a Neocomian uplift of the western flank of the Dandaragan Trough centered on the Beagle Ridge. The extent and magnitude of truncation is reflected in systematic variations in sandstone porosity trends. Vitrinite reflectance data suggest that the uplift and erosion of the Beagle Ridge was accompanied by higher geothermal gradients than measured today in exploratory boreholes. Modern gradients of up to 5.0°C/100 m were measured on the Beagle Ridge and possibly represent this waning geothermal anomaly. In contrast, low geothermal gradients are found in the Dandaragan Trough (around 2.0°C/100 m), and hydrocarbon generation occurs at great depths whe e sandstone reservoir properties are often inadequate for commercial production. Extensive vertical migration of hydrocarbons to shallower levels with better reservoir characteristics may be a prerequisite for producible accumulations in areas with low gradients.