Group lending as a mechanism for self-insuring default risk

We show that banks can provide loans at low costs to high-risk borrowers in the form of a group lending contract in which all members are jointly liable for their loans. By providing such contracts borrowers self-insure against some of the default risk the bank faces. We determine the optimal group size in a competitive banking system and find that it is reasonably small and borrowers internalize an increasing fraction of the risk the higher their risks are.