Natural gas reserves refer to large deposits of natural gas which, based on geological surveys and engineering studies, are thought to exist to a very high degree of certainty. In addition to the knowledge of their existence, these reserves are also accessible and economically viable to extract. Natural gas reserves are spread worldwide, however, some countries have more natural gas than others. It is estimated that the total world reserves amount to around 6 quadrillion cubic feet. Rough estimates suggest that this large reserve is equal to around 6000 exajoules of energy.
One way to think about the size of reserves is known as the reserves/production ratio or R/P. This number represents the number of years that the reserves would last if production and use was continued at the current rate.
Natural gas reserves (and R/P ratios) are smaller than coal reserves but larger than the R/P ratio of oil. Estimates suggest that at the rate of current use, there is around 60 years worth of natural gas remaining. However, this ratio needs to be interpreted carefully as this assumes current production levels. Production has been increasing steadily for the past few years with improved technologies, and may continue to increase. Moreover, this number doesn't take into account changing prices or developments that allow fuel to be extracted from current resources.
Russia has the world's largest natural gas reserves, followed closely by Iran and Qatar. Recently, natural gas has become more and more important as a fuel source as its reserves are so vast. In addition to reserves that exist currently, there is huge potential for more reserves to be found. In addition, some natural gas occurrences are becoming reserves as drilling technologies advance. Recent advances in drilling technology allow natural gas to be extracted by hydraulic fracturing from shale formations. These technologies have been allowing people to extract natural gas from sources that had previously been impossible, which has increased the natural gas reserve.
Below is an interactive graph showing what regions have major natural gas reserves. Note that despite natural gas generally forming along with crude oil, Saudi Arabia has massive oil reserves but is comparable to the United States in its gas reserves. Press the play button on the bottom left to see how the reserves have changed over the past few decades.