Fill or Kill Order (FOK) Meaning

A Fill or Kill (FOK) order is a type of trading instruction that requires an order to be executed immediately and in its entirety, or not executed at all. If the full quantity specified in the order cannot be filled at the requested price (or better) at the moment the order reaches the market, the entire order is automatically canceled. There is no partial execution and no waiting period. This makes FOK orders one of the most rigid and time-sensitive order types used in financial markets, including equities, foreign exchange, and increasingly, cryptocurrency trading.

The primary purpose of a FOK order is to eliminate execution uncertainty. Traders who use FOK orders typically have precise requirements around position size, pricing, and timing. For example, an institutional trader may want to acquire or sell a large block of an asset only if the entire amount can be transacted instantly at a specific price. A partial fill could expose them to market risk, price slippage, or information leakage, especially in less liquid markets.

By using a FOK order, the trader ensures that the trade either happens exactly as planned or not at all. In practice, when a FOK order is submitted, the trading system immediately checks available liquidity across the order book (or across connected venues in more advanced execution environments). If sufficient liquidity exists to fill the full order size at the specified price, the trade executes instantly. If even a small portion of the order cannot be matched, the system cancels the entire order without executing any part of it.

This all-or-nothing behavior distinguishes FOK orders from Immediate or Cancel (IOC) orders, which allow partial fills while canceling any unfilled remainder. FOK orders are commonly used by professional and institutional participants, particularly in algorithmic trading, block trading, and high-frequency strategies. They are useful when precise execution conditions matter more than simply getting into or out of a position. However, this strictness also makes FOK orders harder to execute in volatile or illiquid markets, where available liquidity can change rapidly.

As a result, many FOK orders are canceled without execution, especially when order sizes are large or price limits are tight. In cryptocurrency markets, FOK orders are often employed on centralized exchanges and institutional trading platforms where execution logic is automated and latency is low. They can help traders avoid partial exposure during fast-moving markets or prevent adverse selection when liquidity is fragmented.

That said, because crypto markets can experience sudden liquidity gaps, FOK orders may fail more frequently than in deep, traditional markets. Overall, a Fill or Kill order is a precision tool designed for traders who prioritize certainty and control over execution flexibility. It trades execution probability for exactness, making it a powerful but situational order type.