Quick definition An order that either fills completely at the current market price or is cancelled entirely. No partial fills are accepted. What it is A FOK order is an all or nothing instruction. The order sweeps the opposite side of the book in search of enough liquidity to fill the entire quantity at the specified price (or better). If enough liquidity exists at the current market price, the entire order fills. If not enough liquidity is available, the entire order is cancelled. No partial execution occurs. Why it matters FOK orders are used when a trader must execute a specific quantity or not at all. This is common in block trading and arbitrage. A trader executing a pairs trade must fill both legs or neither leg. FOK orders enforce this all or nothing constraint at the execution level. FOK versus IOC (Immediate-or-Cancel) An IOC order accepts a partial fill. A FOK order does not. Both orders cancel unfilled quantity instead of resting on the book. The difference is whether the trader is willing to accept a partial fill. Practical example A trader wants to buy exactly 5,000 shares of stock A as part of a pairs trade. The trader submits a FOK buy order for 5,000 shares. The best ask has 3,000 shares available at $50.00 and another 2,000 shares at $50.01. The order cannot fill entirely at the best price, so the entire order is cancelled. The trader receives zero shares instead of 3,000. Execution requirements A FOK order requires careful price construction. A trader should set the limit price high enough to absorb the expected depth at the best price level. A FOK market order (no limit price) searches the book at progressively worse prices until enough liquidity is found to fill the entire order, or the order is cancelled. Regulatory considerations FOK orders are supported on most US equity venues (NYSE, Nasdaq, Cboe) and all major futures exchanges. Always verify venue support before submitting a FOK order in a new market. Comparison to All-or-None (AON) An all-or-none (AON) order also requires the entire order to fill, but it may rest on the book and wait for the full quantity to accumulate. A FOK cancels immediately if the full quantity is not available now. See also - Immediate-or-cancel (IOC) - All-or-none (AON) - Good-til-cancelled (GTC) - Market order
