The Opening AuctionBetween 07.50 and a random time between 08.00 and 08.00.30, there will be called an auction period during which time, limit and market orders are entered and deleted on the order book. No order execution takes place during this period so it is possible that the order book will become crossed. This means that some buy and sell orders may be at the same price and some buy orders may be at higher prices than some sell orders.
At the end of the random start period, the order book is frozen temporarily and an order matching algorithm is run. This calculates the price at which the maximum volume of shares in each security can be traded. All orders that can be executed at this price will be filled automatically, subject to price and priorities. No additional orders can be added or deleted until the auction matching process has been completed.
The opening price for each stock will be either a 'UT' price or, in the event that there are no transactions resulting form the auction, then the first 'AT' trade will be used.