Seawater injection into oil reservoirs for purposes of secondary oil recovery is frequently accompaniedby souring (increased sulfide concentrations). Production of hydrogen sulfide causes various problems,such as microbiologically influenced corrosion (MIC) and deterioration of crude oil. Sulfate-reducingbacteria (SRB) are considered to be major players in souring. Volatile fatty acids (VFAs) in oil-field waterare believed to be produced by microbial degradation of crude oil. The objective of this research was toinvestigate mechanisms of souring, focusing specifically on VFA production via crude oil biodegradation.To this end, a microbial consortium collected from an oil–water separator was suspended in seawater;crude oil or liquid n-alkane mixture was added to the culture medium as the sole carbon source, and theculture was incubated under anaerobic conditions for 190 days. Physicochemical analysis showed thatpreferential toluene degradation and sulfate reduction occurred concomitantly in the culture containingcrude oil. Sulfide concentrations were much lower in the alkane-supplemented culture than in the crudeoil-supplemented culture. These observations suggest that SRB are related to the toluene activation andVFA consumption steps of crude oil degradation. Therefore, the electron donors for SRB are not only VFA,but many components of crude oil, especially
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