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Separate immediate execution from full-size execution15 minute read
IOC vs FOK vs AON option orders
Compare immediate-or-cancel, fill-or-kill, and all-or-none option orders, including partial fills, full-size conditions, limit prices, venue support, and multi-leg restrictions.
Direct answer
An immediate-or-cancel order executes any quantity available immediately and cancels the remainder. A fill-or-kill order must execute its entire quantity immediately or cancel without a fill. An all-or-none order requires full-size execution but, in its general form, does not necessarily require immediacy. Broker and venue implementations vary, and some markets accept AON only with IOC, making that combination function like FOK.
IOC accepts an immediate partial fill
Consider an IOC limit to buy ten calls at $2.00 or better. If four contracts are immediately available within the limit, those four can fill and the remaining six are canceled. If all ten are available across eligible interest, all ten can execute. IOC controls duration, while the limit controls the worst price.
A canceled final status does not prove zero contracts traded. It can describe the unfilled remainder after a partial execution. Read the filled quantity, average price, execution reports, position, and buying power before resubmitting what appears to be a canceled order.
FOK requires full size immediately
The same ten-contract FOK limit either receives all ten immediately within the price boundary or receives none. It can reduce the operational problem of carrying an undersized position, but it also rejects useful partial liquidity and therefore can lower execution probability.
Displayed size is not a reservation. It can move before arrival, belong to interest that is not accessible under the route, or fail another order condition. A FOK cancellation does not prove that ten contracts never existed anywhere; it means the order could not complete under its actual terms and handling at that moment.
AON adds a size condition, not always a clock
A traditional all-or-none order says do not execute unless the entire quantity can fill. If paired with a day duration and supported, it can wait for sufficient size. If paired with IOC, it must find the full size immediately or cancel, producing FOK-like economics.
Support is fragmented. AON orders may be non-displayed, restricted to IOC, unavailable for a product, or handled differently by a broker. FOK may be allowed for a simple option but not a complex order on the same venue. The label in one platform does not establish another platform's rules.
Choose the condition from the cost of being incomplete
IOC suits a trader who values immediate information and accepts a smaller position. FOK or an immediate AON condition suits a trade whose fixed costs, hedge ratio, capital use, or risk limits make partial size unacceptable. A waiting AON can preserve the full-size condition but may miss smaller liquidity repeatedly.
Before submission, verify limit price, total contracts, minimum acceptable fill, time in force, routing, display treatment, simple or multi-leg eligibility, and what the broker reports after cancellation. For a spread, a true complex order already preserves leg ratio by strategy unit; adding FOK concerns total strategy units, not allowing unmatched legs.
Common questions
Can an IOC option order partially fill?
Yes. That is its defining distinction from FOK. The immediately available portion can execute within the order's price terms and the balance is canceled. Confirm the filled and canceled quantities separately because the final order row may emphasize the cancellation.
What is the difference between FOK and AON option orders?
FOK combines two requirements: the whole quantity and immediate execution. AON is principally a full-quantity condition and can sometimes rest when paired with a longer duration. However, a venue that permits AON only with IOC makes it behave much like FOK, so support details matter.
Why was my FOK option order canceled when the quote showed enough size?
The quote could change before arrival, displayed contracts might be split across inaccessible interest, other orders could consume them, or the order could fail price, routing, or eligibility conditions. The screen is a snapshot, not reserved inventory. Ask the broker for route and rejection details when the sequence matters.
Can I use FOK or AON on a multi-leg option order?
Do not assume so. Exchange specifications can support IOC for complex orders while excluding FOK, and a broker may expose fewer choices. A complex order can still partially fill in complete strategy units while preserving its leg ratio. Verify whether the size condition applies to total strategy units and whether the selected venue accepts it.
Sources and further reading
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