I would think its the Fed keeping the markets orderly. Or is there some special safety in buying negative yield? http://www.nytimes.com/2010/10/26/business/26bond.html Inflation Bonds Are Sold With Negative Yield for First Time By CHRISTINE HAUSER Published: October 25, 2010 At a time when savers complain that they are earning almost no interest from their bank accounts, some investors on Monday bought United States government bonds that effectively had negative rate of return. Bizarre as it sounds, that is correct. In an auction of a special kind of five-year Treasury bond, investors paid $105.50 for every $100 of bonds the government sold â agreeing to pay the government for the privilege of lending it money.