Investors are buying U.S. government bonds after fresh worries emerged about Spain's economy.
Spain said Monday it was back in recession for the second time in three years. Investors worried that Spain might need a rescue as Greece and Ireland did. But rescuing fourth-largest economy in the 17-country euro zone could prove to be too expensive for Europe's bailout funds.
U.S. Treasurys are viewed as one of the safest investments in the world and usually rise in value when investors are anxious.
The price of the benchmark 10-year Treasury note rose 15.6 cents for every $100 invested. The yield on the note fell to 1.92 percent from 1.93 percent late Friday.
The 30-year Treasury bond rose 9 cents for every $100 invested. Its yield remained flat at 3.11 percent.