Microbial activity in oil and gas environments can pose significant challenges for petroleum production. One of the most well-characterized problems is the anaerobic corrosion of carbon steel infrastructure involving sulfate reducing bacteria (SRB). Several mechanisms have been proposed for microbially influenced corrosion (MIC) by SRB. However there remains a lack of knowledge regarding MIC caused by other microorganisms. In recent years, improved genomic technologies are allowing for the characterization of diversity of microbial communities in field samples. These molecular techniques show that while SRB form a fraction of the community associated with corrosion failures, many other microorganisms are also present. In this dissertation these genomic methods were used to characterize several different environmental samples. From these data, MIC mechanisms were hypothesized and tested in laboratory studies. This led to a new biocorrosion model under anaerobic conditions where hydrogenotrophic acetogens (Acetobacterium), hydrogenotrophic methanogens (family Methanobacteriaceae) and acetotrophic methanogens (Methanosaeta) are growing together. In following experiments, we found that carbon steel was preferentially used over oil organics as an electron donor for communities containing methanogenic and acetogenic microorganisms. This community-based MIC model was expanded upon in subsequent experiments where enhanced activity of hydrogenotrophic organisms was seen in the presence of sulfide and carbon steel. In another environment, bisulfite-disproportionating bacteria (Desulfocapsa) were linked to corrosive sulfur formation in water pipelines. Finally the genomics approach was used to identify several sulfur-cycling microorganisms that were potentially associated with MIC in seawater environments. Through this work, a better understanding of how microbial communities are impacting MIC in different steel-containing environments has been gained. This work has also shown how corrosion mitigation strategies can impact microbial growth. This knowledge can be used to develop monitoring and mitigation schemes to limit MIC associated failures, which would be of great benefit from safety, economic and environmental points of view.