The number of oil and gas company bonds with yields of 10 percent or more, a sign of distress, tripled in the past year, leaving 168 firms in North America, Europe and Asia holding this debt, data compiled by Bloomberg show. The ratio of net debt to earnings is the highest in two decades.

If oil stays at about $40 a barrel, the shakeout could be profound, according to Kimberley Wood, a partner for oil mergers and acquisitions at Norton Rose Fulbright LLP in London. West Texas Intermediate crude was up 3.8 percent to $40.06 a barrel at 8:13 a.m. in New York.

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