US government estimates of the amount of natural gas that can be extracted by fracking may be far too optimistic, according to a new study by the University of Texas (UT) at Austin.

In 2013, the US Energy Information Administration (EIA) issued a report saying that, according to its analysis, shale wells, which require fracking to release their gas, would be productive at current levels for “over 30 years,” that is, at least until 2040.

But researchers from UT’s Department of Petroleum and Geosystems Engineering say shale gas production may peak 20 years earlier, followed by a rapid decline in output. Their findings were reported in a feature story published Dec. 3 in the scientific journal Nature.

The problem, according to the UT researchers, goes far beyond merely running out of natural gas. The researchers warn that the US and many other countries, relying on a long-term availability of inexpensive gas, are investing billions of dollars in vehicles, factories and power plants that depend on gas.

Major proponents of fracking are President Obama in the US and Prime Minister David Cameron in Britain. Obama has boasted that “our 100-year supply of natural gas is a big factor in drawing jobs back to our shores.” And Cameron has dismissed fracking opponents as “irrational.”

But if the UT scientists are right and gas production begins to fall off around 2020, all those billions of dollars put into gas-based vehicles and infrastructure will have been wasted.

The researchers conducted their own analyses of natural gas production at the four leading US shale gas formations: the Barnett in Texas; the Fayetteville in Arkansas, the Haynesville in Louisiana, Arkansas and Texas; and the Marcellus in and around the Appalachian Basin. These four formations provide two-thirds of US gas production.

The UT team then extrapolated future output based on the formations’ geology and the expected market forces, including pricing. Their conclusion: Not only will gas production peak in 2020, output will be cut in half by 2030.

How did the EIA and the UT team reach such different conclusions? The Texas researchers said they simply studied the shale formations in greater detail.

“Resolution matters because each play [group of energy fields] has sweet spots that yield a lot of gas, and large areas where wells are less productive,” Mason Inman writes in Nature. “Companies try to target the sweet spots first, so wells drilled in the future may be less productive than current ones.

“The EIA’s model so far has assumed that future wells will be at least as productive as past wells in the same county,” Inman writes. “But this approach, [UT petroleum engineer Ted] Patzek argues, “leads to results that are way too optimistic.”