An important question facing critical infrastructure owners and operators is how their assets could be made to fail by the various threat actors. Designing, enumerating and analyzing failure scenarios helps explore the assumptions made on the operational side, the value of current mitigations and the need for certain types of protection mechanisms. This chapter describes the formulation of 55 failure scenarios in the natural gas distribution infrastructure. These failure scenarios highlight a range of potential threats across the natural gas infrastructure, from transmission to distribution and home metering. The chapter also describes a multi-pronged approach used to develop failure scenarios for the gas sector and compares them against the scenarios developed for the electric sector. The focus is on the concepts underlying the failure scenarios and their use, the threat model they encompass, and the assumptions, lessons learned and caveats underpinning their creation.