In the illustration below, the cascading sequence of market transaction types demonstrates how publishers move their available inventory from one type to the next to optimize for revenue. An ad impression may first be introduced through a direct sale. A direct sale is a non-programmatic transaction of premium inventory between the advertiser and publisher. If the impression is not purchased, it becomes available at a lesser price through a guaranteed deal. If the impression remains unsold, the price reduction continues as it is offered through a preferred deal, then in a private auction, and lastly in the open auction until it is sold. The entire cascade of events occurs milliseconds before a user loads the web page.