If a stockbroker receives separate orders to buy and sell at the same price at the same time, they must offer the stock in the market at a higher price than the bid. If no higher bid is available, they can execute the two deals at the same time and at the same price.
Opening and Closing Crosses
The Nasdaq gathers and posts data on all buy and sell interest in the two minutes prior to its opening; this information is referred to as the opening cross. Traders can post orders to buy at the opening price or to buy if there is an order imbalance. This dissemination of pricing interest helps to limit disruptions in liquidity.
The closing cross on Nasdaq matches bids and offers in a given stock to create a final price of the day. Traders can place orders that can be either “market at close,” which means buy or sell at the official closing price or “limit at close.”
In the latter case, if the price at the close is better than the specified limit, the deal will be executed at the market price. Nasdaq collects data for the closing cross between 3:50 p.m. and the closing time of 4:00 p.m. Cross orders are executed between 4:00 p.m. exactly and five seconds after 4:00 p.m.