About 20 years ago, an entrepreneur named George Mitchell proved that it was possible to get lots of oil and gas out of parts of the earth long thought to be sucked dry, by injecting liquid at high pressure into a horizontal well below the surface. About 10 years ago, fracking — the common term for this process — began in earnest.

In that short amount of time, fracking in America has turned the energy world upside down. A decade and a half ago, Congress was hand-wringing about impending shortages of oil and natural gas. By the end of 2015, President Barack Obama lifted the ban against oil exports. Today, America is the world’s largest producer of natural gas and is an oil powerhouse, ready to eclipse both Saudi Arabia and Russia.

This has led to muscular claims about American energy wealth. Erik Norland, executive director of CME Group, a derivatives marketplace, calls fracking “one of the top five things reshaping geopolitics.”

This radical change has resulted in widespread concern about the impact of fracking on the environment, about earthquakes and water contamination. But another, less well-known controversy may prove to be more important.

Some of fracking’s biggest skeptics are on Wall Street. They argue that the industry’s financial foundation is unstable: Frackers haven’t proven that they can make money. “The industry has a very bad history of money going into it and never coming out,” says the hedge fund manager Jim Chanos, who founded one of the world’s largest short-selling hedge funds. The 60 biggest exploration and production firms are not generating enough cash from their operations to cover their operating and capital expenses. In aggregate, from mid-2012 to mid-2017, they had negative free cash flow of $9 billion per quarter.