The U.S. drive for energy independence is backed by a surge in junk-rated borrowing that’s been as vital as the technological breakthroughs that enabled the drilling spree. While the high-yield debt market has doubled in size since the end of 2004, the amount issued by exploration and production companies has grown nine-fold, according to Barclays Plc. That’s what keeps the shale revolution going even as companies spend money faster than they make it.
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