Global warming is a major concern of today\'s world that mostly stems from greenhouse gases (GHG) emissions among which methane (CH4) has the second highest potential to cause such a problem. Among various types of discharging CH4 into atmosphere, fugitive emission from the natural gas (NG) supply chain has a significant contribution. In this study, methane emission from the pressure reduction station, distribution pipeline and end user regulating systems (EURSs) was experimentally investigated by a gas detector and a Hi-Flow sampler device. The research was conducted in Mashhad, the second metropolis of Iran; Iran plays a key role in NG reserves and consumptions. The results revealed that the fugitive methane emission from the EURSs is the main source of the GHG emission from the gas distribution network. This source was, then, investigated in detail through the being classified into six components including regulator, union fitting, coupling, locking valve, tee fitting, and elbow fitting. According to the obtained outcomes, the regulator is responsible for the highest emission factor (EF = 754 m3/year) along with the largest contribution (66.62%) in total fugitive methane emission of EURSs. Conversely, the elbow fitting demonstrates the lowest EF (= 134 m3/year) as well as the lowest contribution (0.39%). Additionally, the effect of EURSs lifespan on their EF was studied. The results indicate that the ratio of EF of EURSs with lifespans more than 20 years to mean EF is almost 1.4 while this value is approximately 0.8 for EURSs with lifespans less than 20 years. The results also show that the ratio of EF in different seasons to mean EF decreases as the temperature decreases (colder seasons). At the end, the findings of this research could give useful information about the methane emission from EURSs leading to designing and developing proper mitigation strategies.

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