FORT WORTH — Officials at the Federal Helium Reserve, the source of almost half of the U.S. helium supply and more than a third of the world's, say the reserve could exhaust its supply of the inert, nonflammable, lighter-than-air gas by 2020.

The U.S. Bureau of Land Management is responsible for the helium reserve, which consists of about two dozen wells about 15 miles northwest of Amarillo. The wells draw the naturally occurring, inert, lighter-than-air gas from the ground and feed it into a 450-mile pipeline to Kansas.

"There is just a finite amount of helium out there," BLM Amarillo field office manager Leslie Theiss told the Fort Worth Star-Telegram. "There's only so much we can do. The clock is winding down on this place."

The clock apparently started ticking in 1996, when Congress passed the Helium Privatization Act that called on the federal government to sell off most of its helium by 2015. Officials tell the Star-Telegram that the sell-off is running a little behind schedule but should be complete by 2020.

Helium, however, is not a renewable resource.

"Once it's used up, it's gone," said Rasika Dias, professor and chemistry and biochemistry department chairman at the University of Texas at Arlington. "What we have is what we have."

Helium is the byproduct of the decay of radioactive elements.

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"The earth is 4.7 billion years old, and it has taken that long to accumulate our helium reserves, which we will dissipate in about 100 years," Nobel laureate Robert Richardson told the Star-Telegram.

The most familiar use of helium is to lift balloons and airships, but it's also used in its frigid liquid form to cool MRI machines and to detect leaks in spacecraft. It's also used in the making of computer chips.

The federal government began regulating helium as a strategic material in the mid-1920s, when federal officials realized that it was a safe substitute for hydrogen for lifting dirigibles and other lighter-than-air craft.

The gas was produced in Clay County, just east of Wichita Falls, before production moved to northern Fort Worth, which became the world's only helium source. The Fort Worth plant used up its helium supply by 1929, and the federal government built a helium-extraction plant near Amarillo.

Helium is now produced in Wyoming and such overseas sources as Australia, Russia and the Middle East. Chip Groat, energy and earth resources professor at the University of Texas at Austin, says the United States could become a net importer of helium within the next 10 to 15 years.