An all-or-none order (AON) is an order to buy or sell a stated quantity that may be executed only in full. If the market cannot supply the whole amount at the order's price, no part of it trades. The condition is normally attached to a limit order and is used to avoid partial fills, which can leave a trader with an awkward small position and, at some brokers, a separate commission for each piece.
An AON order differs from a fill-or-kill order in timing. Fill-or-kill must be completed at once or cancelled, while all-or-none can wait, for the day or longer, until enough quantity appears. Because it cannot be matched piece by piece, an AON order usually has lower priority in the order book and may go unfilled even when the market trades at its price. Many electronic exchanges do not accept the condition, and it is most common in less liquid securities.