U.S. Treasurys gained on Monday, led by a sharp rise in the 30-year bond, whose yield dipped to a multiyear low on widening anxieties about Europe's economy and Greece possibly quitting the euro zone.
The yield on the 30-year Treasury was last at 2.62 percent, reflecting a 1-17/32 rise in price, after touching 2.615 percent. That was a low last seen in August 2012.
"It's a risk-off trade we are seeing," said Tom DiGaloma, head of rates and credit trading at ED&F Capital Markets in New York.
Global stock markets were weaker, with Dow Jones Industrial Average off 1 percent in early New York trading. Oil prices hit a 5-1/2 year low.
Prices for benchmark 10-year Treasury notes also climbed, with gains last at 19/32 with a yield of 2.0563 percent, according to Reuters data.