Organic matter in Jurassic and lower Cretaceous sediments from 5 wells in the central Eromanga Basin was studied microscopically. The lower Jurassic Birkhead Formation, upper Jurassic to lower Cretaceous Murta Member and lower Cretaceous Transition Beds were sampled over their entire sections. A qualitative and quantitative analysis of the maceral composition of the dispersed organic matter in each formation was undertaken, and on the basis of this plus coal petrology studies comments are made on the depositional environments of the three source-prone units. A large proportion of the shales comprising the Murta Member are high quality petroleum source rocks containing Type-I and Type-II kerogen. The source rocks of the Birkhead Formation and Transition Beds occur over smaller intervals than in the Murta Member and contain Type-III kerogen. Vitrinite reflectance studies indicate that rank and geothermal gradients vary in a complex fashion along the line of section. This is the result of varying depth of burial, variable thermal input from different parts of the basement and thickness of the pre-Jurassic sedimentary sequence. The Nappacoongee-Murteree anticlinal trend was a source of high heat flow in Jurassic-Cretaceous time.