A Fill Or Kill (FOK) order is an all-or-none order instruction used in market microstructure. It requires that the entire specified quantity be filled immediately at the chosen price; if the full amount cannot be filled at once, the order is canceled. This means there is no partial fill or remaining quantity carried over to a later moment. FOK is distinct from other time-in-force and fill rules, such as Immediate-or-Cancel (IOC), which may execute part of the order and cancel the rest.
When submitted to an exchange or liquidity pool, a FOK order is matched against available liquidity. If enough shares (or contracts) are available at the limit price or better to satisfy the full size immediately, the order is filled at the best prices. If not, the entire order is canceled, and nothing is executed. Because the entire quantity must clear at once, FOK orders tend to attract participation only in more liquid instruments or during moments of tight price competition. They are commonly used by institutions or traders who need certainty of full execution and want to avoid partial fills and the price impact of scaling in.
FOK is a form of time-in-force instruction and is most effective when liquidity is ample enough to clear the full size without delay. In thin markets, FOK orders are more likely to cancel rather than execute, which can result in missed opportunities if price levels move quickly.
A trader places a FOK order for 8,000 shares of XYZ at a limit price of 50.00; if 8,000 shares are available to fill immediately at 50.00 or better, the order is filled; otherwise it is canceled.
All-or-None (AON) Order · Immediate-or-Cancel (IOC) Order · Limit Order · Time-in-Force (TIF) · Liquidity · Market Order · Algorithmic Trading