Gas is a fossil fuel and thus a finite resource.
If current rates of gas consumption remain constant, it is estimated that the world's known conventional gas reserves may be exhausted by the 2070s. At the end of 2014, reserves of UK natural gas were estimated at 105.5 (lower), 211.4 (central) or 350.1 (upper) billion cubic metres.
Diversifying the UK energy mix could reduce our reliance on gas. Improving energy efficiency and prospecting for new reserves would also extend the lifetime of natural gas reserves.
Technological advances in extracting 'unconventional' gas – especially gas trapped in shale has increased global reserves significantly. However, there are some uncertainties about the environmental impact of the chemicals and practices involved in these processes. Unconventional gas extraction has increased in many countries around the world, and the International Energy Agency (in the IEA World Energy Outlook 2014) forecasts that it will form an increasing proportion of total gas supply.
Shale gas is natural gas trapped in formations of shale rock. Pumping water and chemicals underground at high pressure breaks up the rock and releases the gas – a process known as hydro-fracturing. Shale and other unconventional gas reserves, such as coal bed methane and 'tight gas' in sandstone, have been identified in a number of countries.