“…The relative abundances of more and less thermally stable biomarker isomers, or their degree of aromatization, will testify to the thermal maturity of the source rock strata when the oil was expelled (e.g., Seifert and Moldowan, 1978;Mackenzie et al, 1980;Radke, 1988;Farrimond et al, 1998). Finally, after reaching a reservoir (but prior to its discovery and production) crude oil composition can further change due to water-washing by meteoric water, deasphaltening, or biodegradation in the reservoir (Connan, 1984;Seifert et al, 1984;Palmer, 1993;Cassani and Eglinton, 1991. Finally, after reaching a reservoir (but prior to its discovery and production) crude oil composition can further change due to water-washing by meteoric water, deasphaltening, or biodegradation in the reservoir (Connan, 1984;Seifert et al, 1984;Palmer, 1993;Cassani and Eglinton, 1991.…”