Bond investors who helped finance America’s shale boom are facing potential losses of $8.5 billion as oil prices plummet by the most since the financial crisis.

The $90 billion of debt issued by junk-rated energy producers in the past three years has fallen almost 10 percent since crude oil peaked in June. Halcon Resources Corp., SandRidge Energy Inc. and Goodrich Petroleum Corp. have been among the hardest hit as OPEC’s refusal to ease a supply glut pushed prices to a five-year low of $66.15 a barrel last week.

The oil selloff is deepening concern among bond investors that the least-creditworthy oil explorers will struggle to pay their obligations and prompt bankers to rein in credit lines as revenue slumps. Halcon, SandRidge and Goodrich are among about 21 borrowers operating in the costliest U.S. shale-producing regions that will be unprofitable if crude oil falls below $60 a barrel, according to data compiled by Bloomberg.

“We are concerned that there will be defaults and that was even before oil fell as much as it has,” Ivan Rudolph- Shabinsky, a New York-based money manager at Alliance Bernstein Holding LP, said in a telephone interview. “There was too much money going into this space that would have resulted in problems long term -- now that timeline has been accelerated.”

Junk Bonds

The 9.3 percent loss for junk-rated energy debt issued by U.S. and Canadian companies since January 2012 compares with a 1.55 percent decline for the broader U.S. speculative-grade market, Bank of America Merrill Lynch index data show. Halcon Resources’s $1.15 billion of 9.75 percent securities issued in April 2013 have lost 29 percent since June 30, while SandRidge’s $750 million of notes sold in October 2012 have plunged 26 percent, Bloomberg data show. Goodrich Petroleum’s $275 million of debt issued at the start of 2012 has dropped 34 percent.

Scott Zuehlke, a spokesman at Halcon, Daniel E. Jenkins, a spokesman at Goodrich, and Duane Grubert at SandRidge didn’t return calls seeking comment on exposure to oil prices.

Advances in horizontal drilling and hydraulic fracturing, or fracking, have helped U.S. drillers pump the most in three decades. Companies have relied on debt financing to make up for cash shortfalls as they expanded, doubling energy bonds’ share of the high-yield market to 17 percent since 2008, according to a Oct. 14 report by Citigroup Inc.

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