Natural gas (NG) transmission and distribution pipelines play an integral role in the United States (US) energy infrastructure. Various incidents over the past decades have caused growing concern as to the current condition of such pipelines in the US. Significant incidents were analyzed to understand the circumstances and causes to enable one to increase transmission and distribution line safety. Various data sets pertaining to significant US natural gas pipeline failures were analyzed in terms of transmission and distribution (main) pipelines. These categories were individually analyzed to develop an overall understanding of trends. While the report focuses on incidents over the '10 - '17 timeframe, additional analyses are included in the Appendix for two earlier time periods, '97 - '01 and '02 - '09. Only 'significant' incidents were included in the analysis, totaling 3000, and categorized in terms of: number of incidents, fatalities; pipe material; release type; ignition/explosion; location of loss; age of pipe; and cause of incident. Four significant incidents within the distribution sets and three significant incidents within the transmission sets were further analyzed as case studies, seven in all. The case studies were developed to provide an in-depth analysis of events leading to failures, providing additional information gathered by the National Transportation Safety Board (NTSB), Pipeline and Hazardous Material Safety Administration (PHMSA), and additional local utility commissions. Finally, recommendations are made for further work in this area, including comparison of the findings of this analysis with on-going steps by the NG pipeline industry to reduce failures.