The extractable hydrocarbon content of a shale sample taken from the source rocks overlying the gas-bearing sands in the Kudu 9A-2 well is concluded to be an indigenous bitumen. Ratios of homologous series of total aromatic and saturated hydrocarbons support the high maturity levels and the source quality, determined from optical and pyrolysis analysis, but conflict with maturity levels derived from sterane and terpane isomerisation ratios. These biomarkerratios suggest generation at lower maturation levels. The conflicting maturity levels are resolved by a geohistory model which predicts early generation and expulsion from a wet-gas or oil-prone source. Early hydrocarbons were generated from the originally higher quality source rock and were possibly isolated from further hydro-carbon input in silty microreservoirs. The biomarker ratios were thus shielded from further change, although the light and medium gravity total hydrocarbon ratios continued to alter until the present due to increasing maturity, mediated possibly by clay catalysis.