Standard & Poor's has placed more than 1,000 U.S. conduit and fusion commercial mortgage-backed securities deals on "watch negative."

S&P says the move does not represent a change in the expected performance of pools but rather a change in its CMBS criteria.

The main change is a revision of credit enhancement levels in line with an effort to establish ones that enable securities carrying top investment-grade ratings of AAA to "withstand market conditions commensurate with an extreme economic downturn without defaulting." S&P said its analysis has resulted in a AAA credit enhancement figure of 19% for the "archetypical" pool.

"We determined the higher enhancement level based on a number of factors, but primarily on our assessment of potential commercial property value declines in the range of 40% to 50% under conditions of extreme stress, such as during the Great Depression," the rating agency said.

"This represents a major recalibration of our CMBS criteria and is intended to make U.S. CMBS ratings more comparable with ratings in other sectors." S&P also said, "While the new criteria represents a major change in our opinion of what might happen under highly stressful conditions, it does not represent a change in our view of the expected performance of commercial pools under current conditions."

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