Market-on-Opening Order
A market-on-opening (MOO) order is an instruction to execute a trade at the official opening price of an exchange, established through the opening auction process. MOO orders guarantee execution at the opening price without specifying a price limit, ensuring participation in the price discovery event that opens the trading day.
Key takeaways
- MOO orders are matched during the opening auction, which aggregates all pre-market interest to establish an equilibrium opening price.
- Investors use MOO orders to act on overnight information (earnings releases, regulatory filings, macroeconomic data) at the first opportunity of the regular session.
- The opening price is often the most significant single price of the day, incorporating all information accumulated since the prior close.
- MOO orders must typically be submitted before the market opens (pre-market submission window) and cannot be modified or canceled after the opening auction begins.
- Opening imbalances created by MOO orders often produce gap openings that set the tone for intraday trading.
Explanation
The market-on-opening order is the mirror image of the market-on-close order, providing investors with a mechanism to participate in the opening auction — the concentrated price-discovery event that establishes the first official transaction price of the trading day. The opening auction aggregates pre-market buy and sell interest accumulated overnight, incorporating information from earnings releases, after-hours news, futures markets, and overseas trading sessions.
The opening price set by the MOO auction is critically important to market participants. For overnight positions, the opening price determines the P&L on any gaps between the prior closing price and the new open. For news-driven event trades — such as positioning after a surprise earnings announcement — the opening auction is the first opportunity to act on the information within the regulated primary market. Traders who submit MOO orders accept whatever price the auction determines; those using pre-market ECN trading may achieve execution before the open but typically at wider spreads and in thinner liquidity.
The mechanics of the opening auction differ from continuous trading. During the pre-market period, limit orders and MOO orders accumulate in the exchange's electronic order matching system. At the scheduled opening time, the exchange's matching algorithm calculates the price at which the greatest volume of orders can be executed and executes all matchable orders simultaneously at that single price. Remaining unexecuted orders, including limit orders that were not matchable at the clearing price, then join the continuous order book for regular trading.
For institutional investors running systematic strategies, the opening auction is significant because intraday algorithms such as VWAP use the opening price as a key input. A stock that opens sharply higher or lower than anticipated may significantly alter the VWAP benchmark against which the algorithm's performance is measured, potentially generating 'negative VWAP performance' even if the algorithm executed correctly given the new price level.
Example
A technology company reports quarterly earnings after the prior day's close, with earnings-per-share beating consensus by 25% and revenue guidance raised substantially. Institutional investors holding the stock or wishing to initiate positions submit MOO buy orders overnight and before the pre-market deadline. The opening auction for the stock — which closed at $150 — clears at $168 due to heavy buy-side imbalance from MOO orders. An investor who submitted a MOO order is filled at $168, while one who waited to submit a market order in continuous trading after the open may be filled at $171 as momentum buying continues.
Related terms
Clearing Day Order Dual Trading Electronic Communication Network Exchange Liquidity Market On Close Order Market Order Matching Algorithm Order Book Price Discovery Scale Trading