Natural gas, the cleanest and the least carbon-intensive fossil fuel, is expected to play a key role in the transition to a cleaner and more flexible energy system. In the central scenario of the International Energy Agency’s (IEA) World Energy Outlook, natural gas is the only fossil fuel that will maintain its share in the energy mix of the coming decades, mainly supported by policies to reduce air pollution and greenhouse gas emissions. The currently oversupplied gas market and low price environment have resulted in renewed growth of natural gas use for power generation and industrial activities in mature gas economies as well as in newly developing gas markets. However, such a comfortable situation does not prevent security of supply concerns and issues, as shown over the past year through different events. The IEA launched the first annual Global Gas Security Review (GGSR) in 2016 to identify and analyse some critical elements such as physical production flexibility of the LNG infrastructure and flexibility in contractual arrangements. This year’s report updates the major findings regarding these two crucial elements of global gas security and aims to deepen analysis by introducing additional concepts and metrics to develop a more comprehensive assessment of global gas security of supply.