This paper describes natural gas quality variations worldwide and looks forward to predict further changes. The drivers for these changes are presented as gas field depletion, climate change, emissions reduction, sustainability and ‘power-to-gas’ energy storage. Sources of future gaseous fuels are examined as pipeline interconnectors, liquefied natural gas, shale gas, biomethane and hydrogen in natural gas, and these are related to gas interchangeability. Various technologies for natural gas quality monitoring are described and compared. Finally the challenges and opportunities for individuals and companies are proposed and these require innovation and development to be able to anticipate and compensate for fuel supply variations in the future.