A market on close (MOC) is a type of market order which directs that the sale or purchase of stock should occur as close to the end of the trading day as possible. Market on close orders can be used for a variety of reasons and in a variety of ways. Most computer programs which are designed to help people perform financial transactions offer this type of market order as an option when they prepare to buy or sell a stock.
Market orders in general are directives to buy or sell stock, ideally at the best possible price. There are a range of reasons to want a market order to be executed at the close of the trading day. One of the most common is the desire to take advantage of the uptick which can occur at the end of the trading day; if an investor knows that the value of a stock tends to rise at the end of the day, for example, he or she can issue a market order to sell at the end of the day to take advantage of this higher price.
A MOC may also be issued if someone suspects that events which are expected to occur will cause a rise or drop in the price of a stock. For example, if a manufacturer is planning to announce quarterly earnings, a market on close allows an investor to get in or out easily. People may also issue this kind of order when they will not be available at the end of the trading day, and they believe that a stock should be bought or sold as the market is about to close.
On occasion, a situation known as an imbalance can develop. A market on close imbalance happens when a company issues an order to sell or purchase a large volume of stock, and the company's representatives cannot fill the order quickly enough. In this case, representatives publish information about the imbalance close to the end of the trading day, providing people on the trading floor with an opportunity to fill the imbalance. Such imbalances can drive prices up or down as people change positions to take advantage of the imbalance.
A market on close sell order can drive down the price of stock, as it may be unloaded at a low price to fulfill the terms of the order. Buy orders, on the other hand, can push stock prices up as people jockey to fill their market on close orders and other traders are alerted to the situation.