All-or-None Order (AON)

An all-or-none (AON) order is a condition placed on a buy or sell order that instructs the broker to execute the entire order quantity in a single transaction or cancel it entirely. Unlike standard orders that can be partially filled (receiving 300 of 1,000 shares ordered), an AON order ensures you either get exactly what you requested or nothing at all.

AON orders solve a specific problem: partial fills in illiquid stocks can leave investors with awkward position sizes, multiple commission charges (with some brokers), and incomplete execution of their investment thesis. If you want to buy exactly 5,000 shares of a small-cap stock to represent a 2% portfolio position, a partial fill of 800 shares defeats the purpose and may incur additional transaction costs as you try to accumulate the remaining 4,200 shares.

However, AON orders have significant limitations. They are not displayed on the order book, meaning they don't contribute to visible market liquidity and are lower priority than standard orders. In thinly traded stocks — precisely the situation where AON orders seem most useful — the all-or-none requirement may prevent execution entirely if insufficient shares are available at your price. An AON limit order to buy 10,000 shares at $5.00 will go unfilled if only 9,500 shares are offered at that price, even though 95% of the order could have been completed.

Most active traders avoid AON orders due to the execution risk. They are primarily useful for institutional investors making large block trades where partial fills would create operational complications, or for individual investors in illiquid securities where commission structures penalize partial fills. For liquid stocks trading millions of shares daily, AON restrictions add no benefit and only reduce execution probability.