Since 1980, the cash-based securities lending program has evolved to become the prevalent form of collateral management model in the United States. By 2005, U.S.-domiciled insurers, pension funds, mutual funds and corporate treasurers had securities valued at more than $1.25 trillion on loan. This evolution has not come without difficulties. In the 1990s, securities lenders found that a rising interest rate environment suddenly depressed the value of their cash collateral investments, in some cases to the point of loss when lenders were unexpectedly required to return cash deposits to borrowers. A few lenders sustained losses that exceeded the income they had earned over the course of several years, although in several cases agent lenders absorbed the damages in order to protect their franchises.