Sales of corporate bonds in the U.S. doubled this week as relative yields narrowed to the tightest level in more than 17 months.

Xstrata Plc, the world's largest exporter of coal burned by power stations, and New York-based JPMorgan Chase & Co. led at least $39.4 billion of new issues following $19.6 billion in the period ended Oct. 12, according to data compiled by Bloomberg. Sales compare with a 2012 weekly average of $27.8 billion

Borrowing costs on dollar-denominated bonds from the riskiest to the most creditworthy borrowers are hovering at record lows, with average yields reaching 3.6 percent yesterday, Bank of America Merrill Lynch index data show. Companies are issuing debt as opportunities on the calendar free from election- and holiday-related disruptions diminish before year-end, according to BNP Paribas SA's Simon Mayes.