Between 1998 and 2002, about $177.1 billion in new bonds were sold in the U.S. telecommunications sector; less than 10 percent were junk bonds.
U.S. oil and gas companies sold about $350.7 billion in debt between 2010 and 2014, the peak years of the oil-and-gas boom, with junk bonds making up more than 50 percent of all issuance, according to Thomson Reuters data.