A Private Auction is very similar to an open auction, with the difference that publishers got the ability to restrict participation to selected advertisers only.
As the name suggests, this type of auctions is invitation-only. Apparently, they can only bid for an impression after being invited to do so by the publisher. In some cases, advertisers may enable specific advertisers to apply for an invite to participate in private auctions.
Using Private Auctions for the selling of their inventory can provide different benefits for publishers:
- ability to offer premium inventory programmatically to a selected range of premium advertisers
- set specific CPM (cost-per-mille) floor prices for premium ad placements and impressions while generating even higher CPM revenue as a result of an auction
- Streamlining the operation through programmatic platforms such as DoubleClick Ad Exchange by Google
Much like the open auction, publishers or ad exchanges can set a minimum CPM for each advertiser. Again, highest bidder will win the impressions.