S&P Leads Rating Agencies In Subprime Market Share Standard & Poor’s led the three major rating agencies in subprime business at the nine-month mark, an exclusive new analysis by Inside B&C Lending reveals. The analysis shows that S&P rated $87.74 billion in subprime mortgage-backed securities through the end of September, a total equal to 94 percent of the $93.33 billion in total issuance.