A "greenshoe option," also called an over-allotment option, gives the underwriter (usually an investment banking firm) of an issue of stock shares the right to sell more than its initial allotment of the shares if investors' demand exceeds the initial allotment. Greenshoe options help ensure that the underwriter makes the maximum amount of money possible if the share price is initially set too low, and they help to stabilize the price of the security by allowing the underwriter to increase supply to meet demand. The over-allotment is usually up to 15% of the initial allotment.