AMARILLO -- Deep beneath the dry, dusty ground outside this Panhandle city lies something lighter than air: helium.

But the supply of the gas that inflates balloons, cools MRI machines and detects leaks in NASA space shuttle fuel tanks isn't infinite.

There's only so much helium in the world, and some fear that a shortage is coming.

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

Still, nearly two dozen underground wells about 15 miles northwest of Amarillo work round the clock to retrieve helium and pump it to customers connected to a nearly 450-mile pipeline that stretches from the Panhandle through Oklahoma and to Kansas.

This site -- thousands of acres where cows and antelope roam -- is home to underground gas fields and the country's only Federal Helium Reserve.

More than one-third of the world's helium supply comes from this site, including nearly half of the U.S. supply.