Internal corrosion failures in oil and water pipeline networks are frequently implicated from microbiologically influenced corrosion (MIC). Corrosive microorganisms can contribute to potential corrosion risks and metal loss, but their presence does not always correlate to MIC occurring. 22 oil and sludge samples were collected from various crude oil pipelines for microbiological and compositional analyses to verify the quality of the internal pipeline and assess the possible microbial contributions to the corrosion products accumulated within those pipelines. Three pipelines were shown to have very high number of corrosive microbes (sulfate-reducing bacteria and methanogens) in the crude oil they transport. Three sludge samples were detected to contain high wt.% of various iron sulfide compounds, Greigite [Fe3S4], Mackinawite [FeS]), and Pyrite [FeS2]. Two Sludge samples comprised more than 85% of elemental sulfur. Some of the assessed pipelines are currently under monthly monitoring program for microbial activities. If high number of corrosive microbes is persistently detected, enhanced corrosion mitigation measures such as biocide treatment may be implemented.