Treasury bonds (T-Bonds, or the long bond) have the longest maturity, from twenty years to thirty years. They have a coupon payment every six months like T-Notes, and are commonly issued with maturity of thirty years. The secondary market is highly liquid, so the yield on the most recent T-Bond offering was commonly used as a proxy for long-term interest rates in general.[?] This role has largely been taken over by the 10-year note, as the size and frequency of long-term bond issues declined significantly in the 1990s and early 2000s.[?]
The U.S. Federal government suspended issuing 30-year Treasury bonds for four years from February 18, 2002 to February 9, 2006. As the U.S. government used budget surpluses to pay down Federal debt in the late 1990s, the 10-year Treasury note began to replace the 30-year Treasury bond as the general, most-followed metric of the U.S. bond market. However, because of demand from pension funds and large, long-term institutional investors, along with a need to diversify the Treasury's liabilities - and also because the flatter yield curve meant that the opportunity cost of selling long-dated debt had dropped - the 30-year Treasury bond was re-introduced in February 2006 and is now issued quarterly. This brought the U.S. in line with Japan and European governments issuing longer-dated maturities amid growing global demand from pension funds.[?] Since the 1970s the 10 Year Treasury Note and the 30 year fixed mortgage have had a very tight correlation.