SINGAPORE — Starting this month and extending through May, South Korea will resume exploratory drilling in waters off its east coast to find out whether a long-hidden energy resource can be turned into a new wellspring of natural gas. Other major energy users and importers, including the United States, China, Japan and India, are in the midst of similar research and development programs to unlock what they hope will be a treasure trove of methane hydrates on land and at sea. All of them aim to be in commercial production by 2020 at the latest.

Gas hydrates have very high energy yield. One cubic meter of methane extracted from hydrate expands into 164 cubic meters of regular natural gas, the least-polluting of fossil fuels. Gas hydrates are icelike compounds of methane and water molecules, and are so far untapped on large scale. They are concentrated in permanently frozen (permafrost) land zones, such as the Arctic and China's Qinghai-Tibetan plateau, and offshore in sediments on the continental shelf margins of many countries.

The full extent of the global gas hydrate resource is gradually being uncovered. Although there is still much to learn, energy specialists estimate it may amount to between 1,000 and 10,000 billion metric tons — or as much as twice the known reserves of conventional fossil fuels (coal, oil and natural gas).