Post-Pleistocene sediments of San Francisco Bay, California, have been analyzed for the presence of normal paraffin hydrocarbons. Gas-liquid chromatography was used to examine sediment extracts for normal paraffins containing 8 through 13 carbon atoms per molecule (intermediate molecular weights). Liquid-solid chromatography, infrared and mass spectrometry were used to determine in sediment extracts normal paraffins containing more than 18 carbon atoms per molecule (high molecular weights). Knowledge of normal paraffins in recently deposited sediments may be useful in explaining the origin of crude oils.

The results of analyses of sediments of San Francisco Bay show that normal paraffins containing 8 through 13 carbon atoms are probably absent, or each is present in a concentration less than one part per million dried sediment. Concentrations from 3 to 6 parts per million dried sediment were determined for the normal paraffins containing more than 18 carbon atoms per molecule. Among the normal paraffins containing 23-35 carbon atoms per molecule, the relative number of molecules having an odd number of carbon atoms is greater than the relative number of molecules having an even number of carbon atoms.

Normal paraffins of intermediate and high molecular weights are present in most crude oils, but only normal paraffins of high molecular weights were detected in the sediments of San Francisco Bay. In the sediments the normal paraffins containing 23-35 carbon atoms per molecule show a predominance of odd-carbon-number molecules. In crude oils the normal paraffins in the same weight range are distributed so that odd-carbon number molecules and even-carbon-number molecules are present in about equal amounts.

If the sediments of San Francisco Bay are to yield crude oil, changes probably should take place in the molecular distribution of the normal paraffins already present. The ratio of odd- to even-numbered normal paraffins should be reduced so that the odd- and even-numbered molecules are about equally abundant. Also, normal paraffins of intermediate molecular weights probably should be added to these sediments. The additional normal paraffins may be derived from other organic materials dispersed in the sediments.

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