The Cooper Basin is a complex intracratonic basin containing a Permian-Triassic succession which is unconformably overlain by Jurassic-Cretaceous sediments of the Eromanga Basin. Abundant inertinite-rich humic source rocks in the Permian coal measures sequence have sourced some 3 Tcf recoverable gas and 250 million barrels recoverable natural gas liquids and oil found to date in interbedded Permian sandstones. Locally developed vitrinitic and exinite-rich humic source rocks in the Jurassic to Early Cretaceous section have, together with Permian source rocks, contributed to a further 60 million barrels of recoverable oil found in fluvial Jurassic-Cretaceous sandstones.

Maturity trends vary across the basin in response to a complex thermal history, resulting in a present-day geothermal gradient which ranges from 3.0 to 6.0°C/100 m. Permian source rocks are mature to postmature for oil generation and comprise oil/condensate and gas kitchens in separate depositional troughs. Jurassic source rocks generally range from immature to mature but are postmature in the central Nappamerri Trough. The Nappamerri Trough is considered to have been the most prolific Jurassic oil kitchen because of the mature character of the crudes found in Jurassic reservoirs around its flanks.

Outside the central Nappamerri Trough, maturation modeling studies suggest that most hydrocarbon generation followed very rapid subsidence during the Cenomanian. Most syndepositional Permian structures are favorably located in time and space to receive this hydrocarbon charge. Late-formed structures (mid-late Tertiary) are less favorably situated and are rarely filled to spill point.

The high CO₂ contents of the Permian gas (up to 50 percent) may be related to maturation of the humic Permian source rocks and thermal degradation of Permian crudes. However, the high ¹³C of the CO₂ (average, -6.9 per mil) suggests some mixing with CO₂ derived from thermal breakdown of basement carbonates.