Gas hydrates are solid crystalline compounds formed under certain thermo-baric conditions from water (water solution, ice, water steams) and low molecular weight gases. Externally, they look like ice or snow. Under moderate pressure natural gas hydrates exist at the temperatures of up to 20–25 degrees centigrade.

There are man-made and natural gas hydrates.

• man-made hydrates can form in gas production systems: in a downhole zone, a well shaft, gas gathering lines, flowlines, gas treatment and processing systems, as well as in gas trunkline systems. Gas hydrates formation is an adverse phenomenon in the gas production processes. Due to this fact, several methods for preventing and eliminating gas hydrates have been designed and are being elaborated.
• natural gas hydrates can form accumulations which may be economically viable in the long run, and may exist in a dispersed phase. A new type of dispersed gas hydrates was identified in permafrost – relic gas hydrates which were preserved due to the self-conservation effect. In some cases natural gas hydrates are considered as a serious complication which leads to operating problems in drilling and operation of oil and gas wells, floating platforms maintenance, etc.

Some natural disasters and so-called mystic phenomena can be ‘hydrate explained’ (for instance, the Bermuda Triangle).