The maximum yield for an uninsured bond due in 2024 is 6.60 percent.

Insured triple-A bonds are now yielding only 15 to 20 basis points below uninsured bonds, he said, calling that "cheap insurance."

Usually the difference between insured and uninsured bonds is about 1 1/4 percentage points.

Institutions rely on their own credit research, and well-heeled individuals are urged by their advisers to seek the higher yields of uninsured bonds.

An A- rating would require it to pay more than 5.7 percent for uninsured bonds.

The uninsured bonds carried a maximum yield of 6.80 percent on securities maturing in 2008.

Among bonds with longer maturities, yields for uninsured bonds ranged from 8 percent in 2000 to about 8.65 percent in 2010.

The Triborough Bridge and Tunnel Authority plans to sell another $245 million of uninsured bonds about 30 days after this week's sale.

The association also estimates that municipal bond guarantors have saved taxpayers $35 billion in interest that they would have paid on uninsured bonds.

Yields were not changed for most of the uninsured bonds, although some yields were cut by a tenth of a percentage point.