Fed rate hikes are expected to hurt bond prices, which move inversely to yields. Besides the headline GDP figure, analysts said details such as the slight decrease in the core personal consumption expenditures gauge to 0.8 percent spurred demand for Treasurys.
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"The PCE core part of the GDP report was a reminder that inflation is still quite weak, and that adds to a bid in the bonds," said market strategist Lou Brien of DRW Trading in Chicago. He said renewed weakness in inflation could delay Fed rate hikes.
U.S. 30-year Treasury yields hit their lowest in 3-1/2 weeks at 2.84 percent. Long-dated bonds benefited from institutional investors' purchases for the purpose of month-end portfolio readjustments.
"Even small repositioning could have led to this marginal rally in bonds" given a lack of liquidity in the bond market, said portfolio manager Sam Diedrich of PAAMCO in Irvine, California.
U.S. 30-year Treasury yields were set for their biggest weekly decline since mid-March of about 12 basis points, while benchmark 10-year note yields were set for their biggest weekly decline since the week ended April 3 of about 11 basis points. Benchmark yields also hit their lowest level in 3-1/2 weeks, at 2.09 percent. U.S. two-year notes, which are sensitive to Fed rate hike expectations, hit their lowest level in a week at 0.6050 percent.
Benchmark and 30-year yields were still set to post their second straight monthly rise in yields, however.
Price action was muted near the end of trading. U.S. 30-year Treasurys yields were at 2.88 percent, from a yield of 2.89 percent late Thursday. U.S. 10-year notes yields were at 2.12 percent, from a yield of 2.13 percent late Thursday.