12 CFR §7.1017

1. (a)A national bank may lend its credit, bind itself as a surety to indemnify another, or otherwise become a guarantor (including, pursuant to 12 CFR 28.4, guaranteeing the deposits and other liabilities of its Edge corporations and Agreement corporations and of its corporate instrumentalities in foreign countries), if:
   1. (1)The bank has a substantial interest in the performance of the transaction involved (for example, a bank, as fiduciary, has a sufficient interest in the faithful performance by a cofiduciary of its duties to act as surety on the bond of such cofiduciary); or
   2. (2)The transaction is for the benefit of a customer and the bank obtains from the customer a segregated deposit that is sufficient in amount to cover the bank's total potential liability. A segregated deposit under this section includes collateral:
      1. (i)In which the bank has perfected its security interest (for example, if the collateral is a printed security, the bank must have obtained physical control of the security, and, if the collateral is a book entry security, the bank must have properly recorded its security interest); and
      2. (ii)That has a market value, at the close of each business day, equal to the bank's total potential liability and is composed of:
         1. (A)Cash;
         2. (B)Obligations of the United States or its agencies;
         3. (C)Obligations fully guaranteed by the United States or its agencies as to principal and interest; or
         4. (D)Notes, drafts, or bills of exchange or bankers' acceptances that are eligible for rediscount or purchase by a Federal Reserve Bank; or
      3. (iii)That has a market value, at the close of each business day, equal to 110 percent of the bank's total potential liability and is composed of obligations of a State or political subdivision of a State.
2. (b)In addition to paragraph (a) of this section, a national bank may guarantee obligations of a customer, subsidiary or affiliate that are financial in character, provided the amount of the bank's financial obligation is reasonably ascertainable and otherwise consistent with applicable law.