Oilmen are known for using salty language, but even they were shocked by some choice words aimed at them a couple of years ago.

The person uttering them was hedge-fund manager David Einhorn of Greenlight Capital. He charged that the companies leading the U.S. shale fracking revolution were “all hat and no cattle,” failing to meet the basic business requirement of returning more cash to investors than they consumed. The biggest offender, he said, was Pioneer Natural Resources —the “mother-fracker.”

Was he right? The price of an exchange-traded fund that tracks the industry, the Van Eck Vectors Unconventional Oil & Gas ETF, ticker symbol FRAK, has shed half of its value since his presentation. Pioneer actually did somewhat better. But benchmark U.S. oil prices dropped from nearly $60 a barrel at the time to just over $26 the next February and are 30% lower today—a factor that weighs heavily on energy shares.

The heart of his argument is worth examining, though, as U.S. oil output is poised to surpass its 2015 record amid a renewed drilling boom in places like the Permian Basin. Over the past decade—roughly the history of the shale boom and two intervening busts—eight leading U.S. shale producers have collectively generated $414 billion in revenue but had negative free cash flow of $68 billion.

There were signs the industry could break that streak this year as technological innovation and a plunge in service costs brought the break-even oil price down by about a third in some locations. Yet analyst free cash flow forecasts for fiscal year 2017 compiled by FactSet show that cumulative expectations for the same eight companies have dropped from just over $1 billion in February to less than $60 million. The obvious explanation is that oil prices have dropped. A big reason for that, though, is shale’s surprising success which has offset supply cuts by big oil exporters.