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.

Falling Oil

High-yield, high-risk debt is rated less than Baa3 by Moody’s Investors Service and under BBB- at Standard & Poor’s.

West Texas Intermediate crude dropped from a June high of $107.26, falling 17.9 percent in November after the Organization of the Petroleum Exporting Countries decided last week to keep its production target of 30 million barrels a day.

Output in the U.S. will climb to 9.5 million barrels a day next year, the most since 1970, the Energy Information Administration estimated Oct 7. Demand nationwide will slip this year to the lowest since 2012, the government predicted.

Lower oil prices will “affect cash flow but also capital spending, which in turn, affect projected production and cash flow in a downward spiral,” Gary Stromberg and Jan Trnka- Amrhein, analysts at Barclays Plc, wrote in a note to clients dated yesterday.

Borrowing Limits

Because the amount oil and gas companies are permitted to borrow from bank lenders is directly tied to the value of their reserves, falling commodity prices increase the risk they will face a cash squeeze, according to an Oct. 9 report by Spencer Cutter, an analyst at Bloomberg Intelligence in Skillman, New Jersey.

The extra yield investors demand to hold the bonds of energy companies instead of comparable U.S. Treasuries increased to 7.63 percentage points yesterday, more than double the premium in June, Bloomberg data show. The price of crude collapsed 35.7 percent during that period.

The issuance of debt has helped contribute to production growth in the U.S. and falling prices will make it harder for companies to meet their obligations, according to Virendra Chauhan, a London-based oil analyst with Energy Aspects Ltd.

“My sense is we’re just on the cusp of bad news there and we’ll see things get worse before they get better,” David Kurtz, global head of restructuring at Lazard Ltd., said at Beard Group Inc.’s Distressed Investing conference in New York yesterday.