The United States on Tuesday offered to help major economies such as China and India develop shale gas, a rapidly growing sector in North America which U.S. officials bill as a clean alternative.

Twenty nations held two days of talks in Washington in first-of-a-kind shale gas talks initiated by the United States, where some forecast that shale -- a minuscule presence a decade ago -- could dominate the gas market by 2030.

Shale gas comes from deep reserves that were thought inaccessible until the advent of new drilling methods. But costs still are usually above conventional gas, and some environmentalists worry about pollution in drinking water.

U.S. officials believe that developing shale gas would provide fast-growing China and India with a cleaner alternative to coal, a key culprit in carbon emissions blamed by scientists for a dangerous warming of the planet.

In Europe, shale gas could also reduce reliance on energy heavyweight Russia. Last year, a dispute between Russia and Ukraine cut off Russian gas to several members of the European Union.

"The main reasons for doing it are national security and climate security," David Goldwyn, the State Department's coordinator on international energy affairs, said of the conference.

"In Eastern Europe in particular, it's really diversity of supply. It's a national security issue," Goldwyn told reporters. "For China and India, it's both climate security and economic security, because they have large demand for resources and the market is volatile."

Another potential reason -- the United States, and to an extent Canada, have an edge in shale gas. Last year, the United States overtook Russia for the first time in decades as the world's top gas producer.

"In this country it's entirely possible, if things continue on trend, that we would have the ability to export gas extracted from shale, liquefy it and export it overseas," Goldwyn said.

He said U.S. energy companies made presentations during the talks, but that the main focus was on explaining to other countries how to start up on shale gas. "Our goal in this conference was really to be a regulatory conference, rather than trade promotion," he said, describing other delegates as "enthusiastic, but careful" on shale gas.

Copyright Agence France-Presse, 2010