In North America prior to 2006 the sulfur content of diesel fuels averaged about 500 ppm. Recent federal regulations have mandated the use of ultra-low sulfur diesel fuel (ULSD) that contains sulfur levels no greater than 15 ppm. While the lower sulfur content has dramatically decreased toxic sulfur emissions from diesel vehicles other unintended consequences have emerged. In some cases underground storage tanks (USTs) that contain ULSD have experienced severe and rapid corrosion. This corrosion has been reported to present itself in as little as six months and can result in failure of the tanks and components leading to environmental contamination. In 2011 the Clean Diesel Fuel Alliance (CDFA) contracted with Battelle to conduct preliminary studies on the underlying causes for the corrosion in USTs for ULSD. The team analyzed fuel water vapor sediment and corrosion scraping samples from USTs at six retail fueling stations using chemical microbiological (e.g. metagenomics microbial community structure analyses) and physical analyses. In all cases ethanol and acetic acid contamination was detected in the USTs. Further aerobic bacteria whose primary energy pathway results in oxidation of ethanol to acetic acid were also consistently detected. A review of all the data provides a strong case that microorganisms are a primary driver of corrosion in ULSD systems synthesizing caustic acetic acid capable of corroding various components throughout the entire UST. These results suggest further study of microbially influenced corrosion in ULSD systems to elucidate prevention and remediation strategies.