Rights issues, entitlement offers and share purchase plans may be underwritten. This means that an underwriter (usually a broker or bank) is guaranteeing that the amount sought by the company will be raised.
A sub-underwriter may be appointed to take up some or all of the underwriter’s subscription obligation. A sub-underwriter assumes a portion of the risk and usually receives a cash fee for doing so. Sophisticated/professional investors can be invited to bid for sub-underwriting.