Natural gas pipelines carrying a mixture of gas and water have been known to block up, stopping the gas flow. This happens when methane molecules in the natural gas are trapped by frozen water molecules, making a white, ice-like substance that builds up and plugs the pipe. The substance is methane hydrate, a kind of "flammable ice."

Methane hydrate is a crystalline substance like ice, composed of molecules of water and methane. It is stable under low temperatures and high pressure, and is found mainly below permafrost and in geological formations under the ocean depths. If we can extract the methane, we can use it to replace fuels like oil and coal. In the 1970s, scientists around the world began looking into the potential of methane hydrate as a new source of energy.

Sonar surveys indicate that there could be about 7 trillion cubic meters of methane hydrate under the sea around Japan. This is equivalent to a 100-year supply of natural gas for the country. Since about 80% of Japan's energy sources come from abroad, it would clearly be desirable to use this type of energy.

Between 1995 and 2000, basic research was done while searching for methane hydrate in the Nankai Trough off the Pacific Ocean coast, between the Kii Peninsula and Shikoku. The Nankai Trough is an ocean trench paralleling part of the Japanese archipelago. Some methane hydrate was discovered and extracted, reinforcing hopes for future energy supplies and encouraging the Ministry of Economy, Trade and Industry to draw up a 16-year plan called the Methane Hydrate Exploitation Program. The program promotes work in the field from 2001 to 2016 and includes these goals:

Test wells will be drilled at about a dozen sites off the shores of Japan, starting in 2004.

The estimated amount of reserves is enormous, encouraging hope for the future. But questions remain—how much of the estimated 7 trillion cubic meters of methane hydrate off Japan can be recovered, and how much of this can be recovered economically? The program will go nowhere if it is technically impossible to recover more than a tiny fraction of the reserves, or if it costs more to extract and transport methane hydrate than what is paid for oil and natural gas. The potential for global warming must also be addressed—methane hydrate is a relatively clean fuel because it does not emit sulphur oxides when burned, but methane is a greenhouse gas, so we cannot let it escape into the atmosphere.

"Flammable ice" lies hidden under the ocean depths. Researchers continue to search for ways to recover it and use it as a fuel.