Sales of U.S. corporate bonds rose for the second straight week, the first back-to-back gain in three months, as borrowers took advantage of tightening relative yields.

AT&T Inc., the largest U.S. phone company, and Louisville, Colorado-based Zayo Group LLC led borrowers issuing $17.4 billion, a 6 percent increase from the five days ended June 8, according to data compiled by Bloomberg. The extra yield investors demand to hold corporate debt rather than Treasuries with similar maturities narrowed 3 basis points this week through yesterday to 315 basis points, or 3.15 percentage points, according to Bank of America Merrill Lynch's U.S. Corporate & High Yield Master index.

Symantec Corp. joined AT&T as sales reached $6.9 billion on June 11, the busiest start to a week in more than two months. While issuers rushed to the market on growing optimism that financial contagion can be contained following Spain's request for a 100 billion euro ($126 billion) bank bailout, the pace slowed in advance of elections on June 17 in Greece that may determine the future of the euro zone.