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Coals and carbonaceous shales of Middle to Late Miocene age associated with the delta plain to delta front depositional environments are the source rocks for the Lower Kutei Basin oil and gas fields. These source rocks have outstanding generative potential - TOCs of 20% to 70%, hydrogen indices ranging up to 300, and genetic potential yields up to 175 mg/g. The kinetic profile of these source rocks is characterized by significantly lower generative thresholds than conventional source rock types. Oil generation occurs between Ro=0.35 to Ro=0.6, oil to gas transformation occurs between Ro=0.6 to Ro=1.2, and gas generation from kerogen where Ro>1.2.The top of the effective kitchen is defined in terms of onset of significant hydrocarbon expulsion, not in terms of generation Expulsion commences where Ro=O.6, equivalent to the kinetic threshold of the oil-to-gas rcactioii Potentially. earlier expulsion of oil may occur where tectonic stresses lead to fracturing of the source rocks while In the generative stage.The base of thc effcctive hydrocarbon kitchen is interpreted as the top of the hard overpressure zone. The kitchen is up to 3000 feet in thickness and covers a large area located in the Middle to Late Miocene age paleo-depocentre.The charging of deltaic sandstone reservoirs is very efficient, as the source rocks and thc sandstone reservoirs arc contiguous. Migration is largely lateral and ranges from 0 to 10 kilometres in distance. Vertical migration is an important, but subsidiary factor. Trap formation occurred prior to hydrocarbon migration, hence there is high trapping potential. Conversely, the long anticlines that form the giant oil and gas fields also act as migration shadows to areas regionally updip and out of the kitchen, towards the west.The dominant hydrocarbon type in the basin is gas. The gas is interpreted to be a product of oil to gas catagenesis, not of kerogen to gas metagenesis. Oil occurrence is a case of preservation. Oil is found where the reservoirs lie above the oil-to-gas cracking threshold (10,000 feet or Ro=O.6). There are two basic oil types, of common genetic origin, recognized in the fields. The two oil types are characterized by their post-generative catagenesis history into: (A) a waxy crude and (B) a light API oil that is type (A) oil with the heavier carbon components cracked off.