Microbial life can be hindered by the presence of light oil or low molecular weight hydrocarbons. The study focuses on how microorganisms survive in a diluent transporting pipeline, on souring in a field producing light oil, and on inhibition of acetate-utilizing sulfate reducing bacteria (SRB) by light oil. The study of pigging samples from a diluent transporting pipeline showed that microorganisms were able to survive in encrusted nodules where they were protected from the toxic and harsh environment and would contribute to corrosion. The study of water samples from light oil field showed that biocide, tetrakis hydroxymethyl phosphonium sulphate (THPS) could be the source of sulfate in some of these facility waters. Souring by acetate-utilizing SRB was inhibited by the presence of light oil, so in light oil producing operations once oil is removed from the water with sulfate there is a potential of souring and microbially-influenced corrosion.