Fill or kill (FOK) is a time-in-force instruction that combines an immediate execution requirement with an all-or-nothing quantity condition. The order cannot leave a resting remainder or complete only part of its requested quantity.
Full quantity within the limit
Suppose a FOK limit order requests 15 tokens at a maximum of $8 each. If only 12 tokens are immediately available at $8 or better, the entire order is canceled without a fill. If the full 15 are available within the limit, execution can draw on several compatible orders and prices. FOK does not require a single counterparty or one execution price.
The availability test is applied when the venue processes the order. A screen showing sufficient depth before submission does not reserve that liquidity.
Different from accepting a partial fill
An IOC order in the same 12-token scenario could fill those 12 and cancel three. FOK rejects that partial outcome, which can be useful when the requested quantity matters as a whole.
This instruction does not coordinate separate orders across markets or guarantee a successful arbitrage. Price limits, supported products, available balance, and other venue checks still apply.