When creating an assignment, there are two methods available to determine how the assignment will be served: fixed delivery and auction.

The fixed delivery method serves ads based on weight and quotas relative to other assignments. For more information on priority and weight, read Pacing & schedule.

The auction method submits a bid and will serve if it wins against other auction-based ads. You can choose to have bids be entered as a cost per one thousand impressions (CPM) or as cost per click (CPC). You choose the pricing model for a zone when you create it, but you can also switch the pricing model of an existing zone in its Zone Properties window.

In addition to competing against other direct sale ads, the auction method allows direct sale ads to compete against server-to-server and Open RTB auctions, maximizing the revenue potential of each impression.