The high-rate loan data likely understate the potential peril posed by mortgages with low teaser rates. Under federal rules governing disclosure, some subprime teaser loans do not show up as having high rates. Lenders weren't required to report loan-pricing details until 2004.

The relaxation of credit standards by home lenders has been years in the making. The Community Reinvestment Act, a 1977 federal law, prodded banks to extend more credit in communities where they operated. That warmed many of them to lower-income and minority borrowers. The Federal Housing Administration, a New Deal-era mortgage insurer targeting buyers with little or poor credit, began losing market share to aggressive subprime lenders. These commercial lenders usually charged higher interest rates but promised less paperwork, faster approval and no-money-down loans that seemed more affordable to many borrowers.

Ambitious lenders such as Seattle-based Washington Mutual's Long Beach Mortgage, which between 2004 and 2006 made $48 billion in high-rate loans, used armies of outside brokers to push subprime loans into the suburbs. (A company slogan: "The Power of Yes.") The result was a mortgage bonanza that reached every racial and ethnic group, income level and geographic area.

By 2005, a list of subprime-lending specialists compiled by the Department of Housing and Urban Development had grown to 210 lenders, from 141 in 1996. Their combined loan volume grew tenfold during the same period.