Commercial mortgage-backed securities (CMBS) experienced a 2.07% delinquency rate in May as multifamily and retail properties showed weaker performance, driving loan defaults. It marks the highest CMBS delinquency rate ever recorded by Fitch Ratings since beginning its loan delinquency index in 2001. "Defaults on larger loans continue to drive delinquency increases because later vintage transactions have larger loans, many underwritten with now unrealized proforma income, as well as now-depleted debt service reserves and high leverage," says  US CMBS group head Susan Merrick in a media statement today. One of the largest delinquent loans included in the index, Mansions Multifamily Portfolio, was added in the month, accounting for some of the jump from 1.78% at the end of April. The portfolio, worth $160m, consists of four cross-collateralized and cross-defaulted loans, according to the rating agency. Fitch says declining performance, particularly in oversupplied markets, as well as in secondary and tertiary markets, pushed the multifamily delinquency rate to 4.55%, the highest of all property types. Multifamily properties are highly susceptible to default in CMBS during the current economic downturn, according to the rating agency. Write to Diana Golobay. For an in-depth look at CMBS, please see the July 2009 issue of HousingWire magazine. Disclosure: The author held no relevant investment positions when this story was published. Indirect holdings may exist via mutual fund investments.