The risk premium on the Markit CDX North American High Yield Index, a credit-default swaps index tied to the debt of 100 speculative-grade companies, jumped by the most in two months on Wednesday. BlackRock Inc.’s $13.8 billion exchange-traded fund that buys high-yield debt slid to the lowest level in more than two years.

Investors have shunned speculative-grade debt as crude oil plunged to a five-year low, dragging down securities sold by energy companies, which make up one of the biggest components of the corporate-bond market. The extra yield investors demand to hold debentures sold by companies in that sector has doubled in the past three months.

“While the energy sector has clearly led the high-yield market lower, the overall global risk-off theme has effectively poisoned risk sentiment for speculative grade bonds,” Adrian Miller, director of fixed-income strategies at GMP Securities LLC in New York, wrote in an e-mail. “While fundamentals for U.S. high-yield have remained solid, excluding energy, investors are instead choosing to reduce exposure across nearly all industry sectors.”

Swaps Rise

The Markit high-yield gauge rose as much as 20.2 basis points to 375.9 basis points, the biggest surge since Oct. 9. The index typically rises as investor confidence deteriorates and falls as it improves. A basis point is 0.01 percentage point.

BlackRock’s iShares iBoxx High Yield Corporate Bond ETF, the largest fund of its kind, dropped 1.2 percent to $88.77, the lowest level since June 2012. The extra yield investors demand to own energy-company bonds instead of Treasurys has jumped to 942 basis points, up from less than 450 basis points in September, according to data compiled by Bloomberg.

Sabine Oil & Gas LLC’s $350 million of 9.75 percent bonds plunged 22 cents to 49 cents on the dollar, according to Trace, the bond-price reporting system of the Financial Industry Regulatory Authority.

“The high-yield market has priced in a cushion against defaults but not an overly generous one,” Anthony Valeri of LPL Financial Corp. said Wednesday in a research note. “Nothing occurs in isolation, and if higher-rated B and BB rated bonds weaken, the average yield spread may widen a bit further.”

Junk debt is rated below BBB- by Standard & Poor’s and Baa3 at Moody’s Investors Service.