Compositional changes and 13C12C fractionations during the degradation of hydrocarbons by bacteria

Abstract Petroleum was mixed with water from the North Sea in sterile containers under controlled laboratory conditions. The variations in the composition and carbon isotope ratios of the oil fractions and the gaseous hydrocarbons dissolved in the oil were observed as a function of time. The following trends were recognizable: • —The saturated hydrocarbons were preferentially oxidized. • —The remaining alkanes were slightly enriched in 13 C. • —Slight indications for a 12 C enrichment of the asphaltenes were observed during the bacterial degradation of the oil. • —There were no changes in the isotopic composition of the aromatic fraction. • —The longer-chained, gaseous, saturated hydrocarbons were more rapidly oxidized than the shorter-chain-length hydrocarbons. • —Normal pentanes and hexanes were degraded more rapidly than the corresponding branched-chain alkanes. • —Iso-hexanes were more rapidly degraded than cyclo-hexanes.