. we require the borrowers to provide collateral in an amount equal to or in excess of 100% ( 100 % ) of the fair market value of the securities borrowed . the borrowed securities are revalued daily to determine if additional collateral is necessary . in this regard , we held , as agent , cash and u.s . government securities totaling $ 572.93 billion and $ 527.37 billion as collateral for indemnified securities on loan at december 31 , 2007 and 2006 , respectively