A global interest to increase the use of renewable resources has spurred an interest in hydrogen (H-2) gas as an energy carrier. Natural gas (NG) infrastructure has been proposed as a potential storage, transmission and distributions system for renewably produced gaseous H-2 fuel. Introducing H-2 to the NG system has raised concerns about H-2 leakage from the system. In this paper, we theoretically and experimentally examine leakage of H-2, NG and H-2/NG blends and provide experimental evidence that 100% H-2 gas blends leak at the same rate as H-2/NG mixtures and 100% NG in typical existing low pressure NG infrastructure on the customer-side of the meter. We also provide results from experiments conducted in a simulated leak environment that suggest gaseous fuel blends of H-2/NG mixtures and NG leak at the same rate. Additionally, a review of the classical leak analysis literature resulted in the discovery of similar results, though not mentioned in the ture. We assess the efficacy of a commercial mitigation measure to reduce gaseous leakage from piping system known to leak. Finally, a two-step leakage mechanism theory that involves molecular dynamics and a tortuous leakage path with significant wall interactions is proposed to explain the results that suggest H-2 leaks at the same rate as NG in typical low-pressure gas infrastructure. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.