A private marketplace (PMP) is a programmatic auction that a publisher opens only to buyers it has invited. Instead of offering an impression to every bidder connected to an exchange, the seller lists it under one or more deals, each tied to named buyers and a minimum price, and only bids carrying those deals are considered. The arrangement exists because the open auction treats all bidders alike. Publishers wanted a way to reserve better inventory, data and priority for chosen advertisers while keeping the speed of automated buying, and advertisers wanted more certainty about where their money went.

How a private marketplace works

The transaction starts outside the auction. A publisher, or the supply-side platform (SSP) acting for it, creates a deal: a package of inventory such as a site section, an app, a streaming channel or an audience segment, with a floor price, a currency, a list of permitted buyer seats and, sometimes, a list of permitted advertiser brands. The SSP issues an identifier for that agreement, known as a deal ID. The buyer activates the ID inside its demand-side platform (DSP), usually by attaching it to a line item or campaign.

When a user then loads a page or starts a stream that matches the package, the SSP sends a bid request flagged with the deal. The buyer's DSP recognises the identifier, applies its own targeting and bids. If several invited buyers bid, the highest valid offer above the floor wins. Unsold impressions typically fall through to the open auction.

Inside the ad server, private marketplace demand normally sits above the open auction and below guaranteed campaigns. Google Ad Manager, for example, lets publishers rank non-guaranteed deals so that certain buyers are favoured "even when their bids are lower", according to its help centre, with rank one as the highest priority. An "Open Auction optimized" setting removes that ranking and makes every deal compete on cost per thousand impressions (CPM).

The fields in the bid stream

The mechanics are written into OpenRTB, the real-time bidding protocol maintained by IAB Tech Lab and explained in PPC Land's OpenRTB explainer. In version 2.6, each impression in a bid request can carry a Pmp object, which the specification describes as "the private marketplace container for direct deals between buyers and sellers". It has two working fields. The first, private_auction, decides whether outsiders may bid: 0, the default, accepts all bids, while 1 restricts the impression to the listed deals. The second, deals, is an array of Deal objects.

Each Deal object has only one mandatory field, id. The rest set the terms: bidfloor (default 0) and bidfloorcur (default US dollars), an optional auction type override in at, where 1 is first price, 2 second price plus and 3 means the floor is the agreed fixed price, plus wseat for allowed buyer seats and wadomain for allowed advertiser domains. A guar flag marks guaranteed deals. Audio and video deals gained mincpmpersec and durfloors in July 2023, allowing floors to scale with ad length. A winning bid echoes the identifier back in the dealid field.

The specification's own example shows the logic. A 300 by 250 banner carries an impression floor of USD 0.03, but private_auction is set to 1 and two deals are attached: one for a seat called Agency1 with a USD 2.50 floor under first-price rules, and another for Agency2 at USD 2.00 under second-price rules.

IAB Tech Lab's implementation notes ask DSPs to return at least one deal bid and two open market bids where both are valid, calling "1+1" the minimum and "M+N" the ideal. They also list anti-patterns, including bidders or exchanges "silently applying margin discounts" to deal bids, which can stop a deal from delivering.

Origin and evolution

Private marketplaces grew out of the early ad exchanges. On September 15, 2011, Google introduced Direct Deals on DoubleClick Ad Exchange (AdX), letting publishers offer inventory "to specific buyers at a fixed price" with "first look" access before the open exchange. Google had bought Admeld, a sell-side firm known for its private exchanges, the same year. Preferred Deals followed in 2012, and Private Auctions, which allowed roughly a dozen buyers to compete at a priority above the open auction, entered beta in December 2012 and opened to all AdX participants in April 2013, according to AdExchanger.

Terminology came next. In September 2013 the IAB's Programmatic Publisher Taskforce, chaired by Alanna Gombert of Conde Nast, defined four transaction types. The third, the invitation-only auction, was one in which "a publisher restricts participation to select buyers/advertisers", and the paper listed private marketplace, private auction and closed auction as alternative names. The open auction, by contrast, was "the Wild West of auctions". OpenRTB 2.2, released in April 2014, then added "new enhancements for private marketplace direct deals", fixing the pmp and Deal objects into the standard.

Later changes addressed scale and data. Curators, third parties that package inventory and audience data from many sellers into one deal ID, borrowed the PMP plumbing. IAB Tech Lab released a Deals API for comment on December 5, 2025, and it was marked final at version 1.0 on February 6, 2026, with fields naming the seller, origin and curator and the type of curation fee.

Why it matters

Private deals now carry most programmatic money in several channels. More than four in five US programmatic display ad dollars transact through programmatic direct and private marketplaces, according to EMARKETER's H1 2025 forecast. Bid streams show it too: Jounce Media's March 2025 analysis of 1.5 billion bid requests from 44 exchanges found only 18.6% were pure open auction, with an average of 3.5 deal IDs per request, as PPC Land's curation explainer records. The World Out of Home Organization's 2026 expenditure study, which used revenue data from 12 SSPs aggregated by PwC, put private marketplace transactions at 75.7% of global programmatic digital out-of-home (pDOOH) spend in 2025, a figure the organisation describes as indicative rather than audited. Among buyers, preference for PMP deals was projected to rise from 30% in 2024 to 50% by 2026 in a VIOOH survey of 1,050 advertisers and agencies.

Television has become the clearest example. Comcast Advertising made linear inventory biddable through private marketplaces on October 23, 2025. Mozilla opened its New Tab inventory through private marketplace and programmatic guaranteed deals with Index Exchange in October 2025. Sensitive inventory uses the same route: OpenX's Child-Safe Marketplace, audited by the COPPA safe harbour PRIVO, runs children's connected TV (CTV) inventory only through invitation-only private deals with individually approved buyers and publishers.

Limitations and disputes

Delivery is the most common complaint. The Trade Desk said in June 2025 that 90% of deal IDs fail to scale effectively, an internal figure that has not been independently verified. Magnite's Nick Allen has said that "two-thirds of deals are configured with the desired supply, yet deliver no or very little revenue." Common causes include floors set above market, overlapping deals splitting the same supply and buyers bidding under the wrong identifier.

Setup is slow. Before LinkedIn data can be activated through Microsoft Monetize, buyers must supply a seat name and ID, and deal generation can take up to five business days.

Transparency is the third dispute. A deal ID shows neither who packaged the inventory nor what they charged. Jounce's April 2025 fee benchmarks found about half of curated deal IDs carried no extra fee, about 34% a percentage markup with a median of 14% and about 10% a fixed CPM fee with a median of USD 0.48. Whether curation is new or "rebranded PMP" remains contested: at IAB Europe's July 3, 2025 programmatic day, Comcast's Stephanie Briec said broadcasters had "always been doing curation".

Definitions also conflict. The IAB's 2013 paper equates private marketplace with the invitation-only auction alone and classifies fixed-price preferred deals separately. Google Ad Manager's help centre instead uses PMP as an umbrella for "non-guaranteed programmatic deals", covering both Preferred Deals and Private Auctions.

Private marketplace versus adjacent terms

Open auction. Any eligible buyer may bid, and the real-time bidding auction decides on price alone. In OpenRTB terms, private_auction is 0 or the pmp object is absent.

Preferred deal. One buyer gets first look at a fixed price, with no guaranteed volume. Under Google's usage it is a type of PMP; under the IAB's 2013 taxonomy it is a separate "unreserved fixed rate" transaction.

Programmatic guaranteed. Price and volume are both agreed in advance, and the buyer is expected to buy. The guar flag set to 1 marks it, and PPC Land's programmatic guaranteed explainer covers it in full.

Deal ID. The identifier for one agreement, not the marketplace itself. A single PMP can contain many deal IDs.

Recent developments

The plumbing is being automated. Google's Display & Video 360 roadmap listed April 2026 for retiring manual non-guaranteed deal creation, leaving synchronisation through the seller's platform as the route in. IAB Tech Lab's June 2026 programmatic auction definitions include a seller check that "bids with deal IDs conform to deal terms".

AI agents are the newest buyers. AAMP 2.0, IAB Tech Lab's agentic advertising protocol suite, added agentic private marketplaces among five new transaction types in April 2026. DataBeat found agentic buyers took part in 86% fewer auctions than conventional buyers in May 2026 data, a pattern PPC Land read as consistent with deal-based buying.

The boundary with the open market is also moving. On July 20, 2026, Netflix inventory became available in The Trade Desk's always-on marketplace deals with no minimum spend, alongside the one-to-one PMP and programmatic guaranteed routes that previously required scale commitments.

Timeline

  • September 15, 2011 - Google launches Direct Deals on DoubleClick Ad Exchange, offering fixed-price first-look access to chosen buyers.
  • 2011 - Google acquires Admeld, a sell-side platform known for private exchanges.
  • 2012 - Google launches Preferred Deals on AdX.
  • December 2012 - Private Auctions enter beta on AdX.
  • April 2013 - Private Auctions open to all AdX buyers and sellers.
  • September 2013 - IAB Programmatic Publisher Taskforce defines four transaction types, naming the invitation-only auction as the private marketplace.
  • April 2014 - OpenRTB 2.2 adds private marketplace direct deal enhancements.
  • July 2023 - OpenRTB 2.6 update adds mincpmpersec and durfloors to the Deal object.
  • March 2025 - Jounce Media finds 18.6% of sampled bid requests are pure open auction.
  • June 2025 - The Trade Desk says 90% of deal IDs fail to scale.
  • October 23, 2025 - Comcast Advertising opens linear inventory to private marketplace bidding.
  • December 5, 2025 - IAB Tech Lab releases the Deals API for comment.
  • February 6, 2026 - Deals API 1.0 marked final.
  • April 2026 - AAMP 2.0 adds agentic private marketplaces.
  • June 26, 2026 - IAB Tech Lab publishes final programmatic auction definitions.
  • July 20, 2026 - Netflix inventory joins The Trade Desk's always-on marketplace deals.
  • September 22, 2026 - WOO study puts PMP at 75.7% of 2025 global pDOOH spend.
  • October 5, 2026 - OpenX launches its PRIVO-audited Child-Safe Marketplace.

Summary

Who. Publishers and their SSPs create private marketplaces; agencies, advertisers and increasingly AI buying agents bid in them through DSPs; curators package inventory from many sellers into the same structure; IAB Tech Lab maintains the standards.

What. An invitation-only programmatic auction in which a seller restricts impressions to named buyers through deals carrying floors, seat lists and identifiers, sitting above the open auction in priority.

When. Born in ad exchange products in 2011 and 2012, named by the IAB in September 2013, standardised in OpenRTB 2.2 in April 2014, and extended to curation, linear television and AI agents between 2024 and 2026.

Where. In the pmp object of OpenRTB bid requests and in the deal settings of ad servers, SSPs and DSPs, across display, video, CTV, audio and digital out-of-home.

Why. It gives sellers control over who buys and at what minimum price, and gives buyers access to inventory and data the open auction does not offer, at the cost of setup friction, frequent under-delivery and limited fee transparency.