Private Auctions provide publishers more control over how their inventory is sold, and provide buyers an advantage in auction buys. When the publisher initiates a Private Auction, they invite specific buyers to participate.
Private Auctions make a portion of publisher's non-guaranteed inventory available to the selected buyers at specific minimum prices. The seller and/or Google may set a minimum CPM for each buyer.
The winners of impressions are determined using the Ad Exchange auction model. If an impression qualifies for a Preferred Deal, the buyer gets the impression at the Preferred Deal price. Private Auction bidders do not participate.
Learn more about the differences between the Open Auction, Private Auctions, and Preferred Deals.