What is an open auction?
An open auction is a programmatic marketplace where publishers make ad impressions available to any qualified buyer, and buyers bid on each impression in real time. It is also called the open exchange or open marketplace. There is no pre-agreed price or buyer list: the publisher sets rules like floor prices and blocked categories, and the highest valid bid wins.
It is the largest and most accessible source of programmatic inventory, covering web, app, video and a growing share of CTV.
How an open auction works
A user loads a page or app with an ad slot.
The publisher's SSP, often through header bidding, sends a bid request to one or more ad exchanges.
Connected DSPs evaluate the request using their targeting and bidding settings.
Each DSP that wants the impression submits a bid within milliseconds.
The highest bid above the floor wins. Most exchanges now run first-price auctions, so the winner pays what it bid.
The winning ad is served and the impression is counted.
All of this happens through real-time bidding, usually in a fraction of a second. The publisher controls floors, blocked advertiser categories and creative rules in its SSP, while the buyer controls bids, targeting, brand safety settings and which exchanges or domains to include or exclude.
Why the open auction matters
The open auction gives advertisers scale and flexibility. Anyone with a DSP seat can buy, there are no deal negotiations, and campaigns can start quickly. Prices are set by demand, so CPMs are often lower than in private deals. That makes it a good fit for broad reach and prospecting, as long as quality controls are in place.
The tradeoffs are quality and control:
Inventory quality varies widely, from premium sites to low-value pages built only for ads.
Exposure to ad fraud, low viewability and unsafe content is higher without filters.
Publishers may limit the data passed in bid requests, which makes targeting less precise.
Good open auction buying uses inclusion or exclusion lists, brand safety and fraud filters, viewability targets and supply path rules to keep the scale while cutting the waste.
Open auction vs private marketplace
A private marketplace (PMP) is an invite-only auction. The publisher chooses which buyers can bid, usually sets a higher floor price, and grants access through a Deal ID. PMPs offer more premium and transparent inventory at a higher price. The open auction offers broader reach at lower cost with more quality risk. Many campaigns use both: PMPs for key publishers and the open auction for scale. Open auction prices also move with demand, so CPMs can rise in busy periods like the end-of-year holidays.
Open auctions with AdGeeks
AdGeeks buys open auction inventory through DV360 and Adform, with senior traders setting brand safety, fraud and viewability controls before launch. During the campaign we review placement and exchange reports, cut weak sources and shift budget toward the domains and deals that perform, so open auction reach does not come at the cost of quality.
