Crystallized natural gas — hydrates
Huge quantities of natural gas (primarily methane) exist in the form of hydrates under sediment on offshore continental shelves and on land in arctic regions that experience permafrost, such as those in Siberia. Hydrates require a combination of high pressure and low temperature to form.
In 2010, the cost of extracting natural gas from crystallized natural gas was estimated to be as much as twice the cost of extracting natural gas from conventional sources, and even higher from offshore deposits.
In 2013, Japan Oil, Gas and Metals National Corporation (JOGMEC) announced that they had recovered commercially relevant quantities of natural gas from methane hydrate.