Manufacturers and users of helium are expressing concern about the impending closure of a vast aquifer of the noble gas near Amarillo, Texas.

For around 50 years, the Amarillo site, a natural limestone-walled rock formation covering 13,900 acres and currently holding 10 billion cubic feet of helium, has served as an emergency source of gas when supply is interrupted. At times it has held as much as 30% of global reserves.

Amarillo has its origins in the space race of the 1960s. After the Cold War eased, the US Bureau of Land Management (BLM) began to sell reserves in 1996, and the aquifer's closure is now scheduled for September 2021.

But with only about 15 helium sources globally, the phase-out further increases the risk of supply shortages and higher prices, according to major players in the $2.7 billion market.

Two of the largest industrial gas producers, Linde and Air Liquide, are racing to tap other helium resources. Along with Qatar and Siberia, the companies also are looking at Iran's potential, as IHS analyst Ralf Gubler told the news agency Bloomberg. Iran, which along with Qatar has access to a field that straddles the border, could emerge as a fourth major source within the next 10 years, he suggested.

The most recent helium shortages have convinced producers that security of supply is becoming increasingly important, Nick Haines, head of Linde's helium business told Bloomberg, adding, "there's only one place in the world where it's possible to store large volumes, and that's in the BLM system in Amarillo."

BLM estimates that demand for helium is growing at 5-6 % a year.

With reserves tightening, manufacturers of magnetic resonance imaging scanners, which use helium as a coolant, are said to be asking gas producers to provide more efficient recycling equipment for helium.