DEFINITION of Stock Ahead
Stock ahead refers to a situation in which an order is placed, but not executed, because of a previously sent order involving the same price. Depending on the exchange's priority rules, this can also happen when two bids are made at the same time with identical prices; only the larger order will be executed.
BREAKING DOWN Stock Ahead
Stock ahead refers to the queue of orders waiting to be executed. When orders are waiting to be executed, the orders that have an executable price that arrived in line first will be given priority. The other orders may have to wait to be executed because there was "stock ahead" of them in the queue.
Example of Stock Ahead
Bert and Ernie each place an order for XYZ stock at the same time. Bert places an order to sell 1,000 shares at $50.00/share. Ernie places an order to sell 500 shares at $50.00/share. Due to the exchange's priority rules, Bert's order for 1,000 shares is given priority and executed due to its larger size. Ernie's order for 500 shares would not be filled at that time because there was a "stock ahead."
In another scenario, Bert places a limit order to sell 1,000 shares of XYZ stock for $50.00/share. The price hasn't moved such that Bert's order can yet be filled. While his order is waiting, Ernie sends a limit order to sell 1,000 shares of XYZ stock for $50.00/share. When the price eventually rises to $50.00/share, there are only enough shares available to complete Bert's order. Ernie's remains unexecuted because there was "stock ahead."