United Technologies Corp.'s $9.8 billion offering, the largestin more than three years, sent U.S. corporate bond saleshigher last week even as speculative-grade issuance plummetedto the lowest levels of 2012.

Overall issuance soared 38 percent from the previous week to$19.4 billion while junk bond sales declined 60 percent to $1.9billion, according to data compiled by Bloomberg. Hartford,Connecticut-based United Technologies, which last tapped the marketmore than two years ago, sold debt in six portions ranging from18-month floating-rate notes to 30-year bonds.

Bond buyers are being lured by higher-rated debt like that ofthe maker of Sikorsky helicopters and Pratt & Whitney enginesas turmoil in Europe sends them to safer assets. Whileinvestment-grade returns in the U.S. are down 0.2 percent thismonth through yesterday, speculative-grade bonds have declined 1.3percent, according to Bank of America Merrill Lynch index data.