(USA) An underwriting arrangement in which an underwriter agrees only to use its best efforts to sell the securities as the issuer's agent. The underwriter does not purchase the securities itself and has no obligation to purchase any amount not purchased by investors. In the UK, such a limited duty of an underwriter would be described as being on a 'reasonable endeavours' basis. See 'All-or-None' and 'Firm Commitment Underwriting'.