natural gases and 130 core samples from potential source rocks enable resolution of the generation and migration history of petroleum in the Bowen and Surat basins. Biomarker analysis confirmed a pre-Jurassic source for the petroleum.Stable carbon-isotope analysis further indicated a Permian-sourced petroleum and was able to differentiate a very minor and localised Triassic source contribution.The dominant source for the petroleum is terrestrial land plants as well as a minor marine source influence. Lower delta plain and alluvial Permian coals show thehigher liquid potential compared with upper delta plain facies. Initial liquid expulsion from the source rock occurred at vitrinite reflectance 0.65-0.7% and continued to Ro of 1.05%. This was followed by the main phase of gas generation between1.05c/o