A simple order book is an order book that only contains the basic components: sizes and prices. It is a simple electronic list of buy or sell orders of securities arranged as per price levels and time priorities. A trader with a higher price on the buy side or lower price on the sell side will be assigned priority over traders in terms of execution/ filling as per current, price level priorities.

The following table provides an example of a simple order book with best bid at 42.75 and best ask at 42.85.