The energy source of the future may lie beneath the ocean floor and under Arctic permafrost, scientists say.

Both places are sources of gas hydrates, strange icelike substances that trap methane-the primary component of natural gas.

"It's not frozen gas," explained Timothy Collett of the U.S. Geological Survey in Denver. "It's [formed] from the interaction of gas and water."

The hydrates were discovered in 1983, and no one knows how many of them exist.

But there appear to be enough hydrates to represent a larger energy source than all of the word's gas, oil, and coal combined, Collett said at a meeting of the American Physical Society in Denver, Colorado, on March 5.

Twenty-three percent of the Earth's surface is covered by permafrost and may have hydrates beneath it, he said, and most of the world's oceans are deep enough for hydrates to exist just under the seabed.

Most deep-sea hydrates are likely to be found near the margins of continents, he added.

Because each cubic foot (0.02 cubic meter) of hydrate releases 160 cubic feet (4.5 cubic meters) of natural gas, "they're a very good storage system for methane," Collett said.

Hydrates are being studied as a fuel source not only in the U.S., which is looking for an alternative to foreign oil, but in India and China, whose burgeoning economies need a new energy source.

Japan and Korea are also interested, Collett said.

Efforts to extract the methane are focusing on the Arctic, where tests have shown that gas can be produced from hydrates using conventional drilling and production technology.

Rather than mining solid hydrates, scientists are working on ways to melt the deposits underground. This would free the gas from the ice, allowing the methane to be captured in the same way ordinary natural gas is collected.

More research has to be done to determine how to extract methane safely and efficiently from hydrates' remote locations, scientists say.

Currently most research is focusing on where and how hydrates form.

Michael Riedel of Canada's McGill University in Montreal says that hydrate formation appears to be much more complex than scientists had previously thought.

Based on samples drilled near the coast of Vancouver Island in British Columbia, he said, hydrates appear to be concentrated much closer to the surface of seabeds than previously believed (see British Columbia map).

Hydrates appear to form only in sandy sediments, he added. This may make it hard to estimate how many hydrates are in a region without knowing where the sandy deposits are, he explained.

"They can't just form anywhere," Riedel said.

Global Warming

Other scientists are trying to understand how hydrates might affect the environment.

Because methane is a powerful greenhouse gas, some experts wonder if massive methane releases from melting seabed hydrates might have contributed to past epochs of global warming.

Others are concerned that current global warming may heat the oceans enough to melt the hydrates, causing similar methane releases today.

Unstable hydrates could also cause underwater landslides, which could damage offshore drilling equipment and possibly create surges large enough to generate tsunamis, according to some models.

Earthquakes pose an additional risk, added Riedel, the McGill scientist.

At a meeting of the American Geophysical Union last December, he compared the effects of quakes on hydrates to shaking a bottle of soda.

"You can get a lot of gas out of it at once," he said.