U.S. companies are issuing bonds at the fastest pace ever. Andinvestors say the Federal Reserve's next rate hike may do little tochange that.

Investment-grade companies are on track to complete the busiestfirst quarter for debt sales since at least 1999. Firms from AppleInc. to Morgan Stanley have pushed new issues to more than $360billion so far in 2017, closing in on the previous record of $381billion from 2009, according to data compiled by Bloomberg. Thatputs bond sales 17% ahead of last year's record pace.

Low borrowing costs, rising stock prices, positive economic dataand strong quarterly earnings results have all helped fuel theboom, said Dominic Pappalardo, a money manager at McDonnellInvestment Management, which manages $11.5 billion. The extrayield over Treasuries investors demand to purchase the bondshas reached multi-year lows in recent weeks, even ascompanies such as Delta Air Lines Inc. to Walt Disney Co. havesold more than $77 billion of bonds to investors so far inMarch.