![[https://m.wsj.net/video/20181203/120318yellowjackets/120318yellowjackets_167x94.jpg]](https://m.wsj.net/video/20181203/120318yellowjackets/120318yellowjackets_167x94.jpg)
The rapid decline of U.S. oil prices will test the claim of fracking companies that they can now prosper at $50 a barrel or less, a price level they have found challenging in the past.
For years, the companies behind the U.S. oil and gas boom, including Noble Energy Inc. and Whiting Petroleum Corp., have promised shareholders that they have thousands of prospective wells that they can drill profitably even at $40 a barrel. Some have even said they can generate returns on investment of 30%....
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