The open exchange vs private marketplace programmatic decision is usually framed as cheap against expensive. Open exchange display clears at $2 to $8 per thousand impressions, private marketplace display at $10 to $25, and a finance team comparing those two lines will ask why anyone pays three times as much for the same banner. The answer is that the two are different products, and the rate is only the first of four numbers that determine what an advertiser pays for an impression that could plausibly produce a customer.
This article compares the two buying methods on price, quality, scale, and control, works through the effective-cost arithmetic, and gives a rule for dividing budget between them. It is written for marketers selling products with long consideration periods and small qualified audiences, where the difference matters most.
What Is the Difference Between Open Exchange and Private Marketplace Programmatic?
Both are auctions run in real time through the same technology. They differ in who is allowed to bid and what is known in advance.
Open exchange (also called the open auction or open marketplace) is available to any buyer with a demand-side platform. A publisher makes an impression available through one or more exchanges, every eligible advertiser can bid, and the highest bid wins. The buyer does not negotiate with the publisher and often does not choose the publisher at all; the platform's algorithm selects impressions that match the targeting and price settings.
Private marketplace, or PMP, is an invitation-only auction. A publisher, or a group of publishers, packages specific inventory and offers it to selected buyers under a deal ID, with a negotiated minimum price. Only buyers holding that deal ID can bid. The buyer knows which publisher and which sections or programs are included, and usually receives priority over open exchange demand in the publisher's ad server.
| Open exchange | Private marketplace (PMP) | |
|---|---|---|
| Who can bid | Any buyer | Invited buyers with a deal ID |
| Price | Set by auction; low floors | Auction above a negotiated floor |
| Publisher known in advance | Often no | Yes |
| Priority in ad server | Lowest | Above open exchange |
| Publisher's own audience data | Rarely available | Often included |
| Setup | None | Deal negotiation and troubleshooting |
| Typical site count per campaign | Thousands to tens of thousands | Tens to low hundreds |
| Volume guarantee | None | None (that requires programmatic guaranteed) |
A private marketplace does not guarantee delivery. Buyers who need a fixed number of impressions at a fixed price use programmatic guaranteed, a third method outside the scope of this comparison.
Open Exchange vs Private Marketplace Programmatic on Price
Rates vary by format, season, and targeting. The ranges below are Stillwater planning benchmarks for US campaigns before data and platform fees.
| Format | Open exchange CPM | Private marketplace CPM | Typical PMP premium |
|---|---|---|---|
| Standard display | $2 to $8 | $10 to $25 | 2x to 4x |
| Online video (in-stream) | $10 to $20 | $20 to $40 | 1.5x to 2.5x |
| Connected TV | $15 to $28 | $30 to $55 | 1.5x to 2.5x |
| Streaming audio | $8 to $15 | $18 to $35 | 1.5x to 2.5x |
| Native | $3 to $9 | $10 to $22 | 2x to 3x |
Fourth-quarter rates run 20 to 40 percent above these in most categories.
The premium has three sources. The publisher sets a floor above what the open auction would clear, because the inventory is its better positions and programs. Fewer intermediaries are involved, so a larger share of the price reaches the publisher. And first-party audience data, when included, is priced into the deal instead of billed separately.
That last point changes the comparison. An open exchange buy aimed at wealthy households needs third-party audience data, which commonly adds $1.50 to $6.00 per thousand. On a $4 display impression, data can double the cost before a single quality question is asked.
Open Exchange vs Private Marketplace Programmatic on Quality
Price per thousand impressions served is the wrong denominator. What matters is price per thousand impressions that were seen by a person, in an acceptable setting, in the intended audience. Each condition removes a share of the impressions bought.
What the supply chain studies found
The most cited evidence comes from the Association of National Advertisers. Its 2023 study of US open-web programmatic spend found that the average campaign ran across about 44,000 websites, that made-for-advertising sites took roughly 21 percent of impressions and 15 percent of spend, and that after fees and unproductive impressions about 36 cents of each dollar entering a demand-side platform reached a consumer effectively. The study's central recommendation was to cut site lists sharply and buy more through private marketplaces and direct deals.
In the UK, ISBA and PwC traced advertiser money through the programmatic chain and found that about half reached publishers in their 2020 study, rising to about 65 percent in the 2022 follow-up as transparency improved.
These studies describe averages across large advertisers. A carefully managed open exchange campaign does better than the average. Still, they show where the losses sit, and nearly all of the categories are open exchange phenomena.
Four quality rates to compare
| Quality factor | Open exchange (no inclusion list) | Private marketplace |
|---|---|---|
| Viewability (display) | 50% to 65% | 70% to 85% |
| Invalid traffic after pre-bid filtering | 1% to 4%; higher in CTV | Under 1% typical |
| Share on made-for-advertising or low-quality sites | 5% to 20% | Near zero |
| Share reaching the intended affluent audience | 10% to 25% with third-party data | 35% to 60% with publisher data and overlay |
| CTV: share on the declared premium app | Variable; misdeclared apps are a known risk | High; publisher-sold |
Ranges are planning assumptions informed by verification reporting across campaigns and should be confirmed with your own measurement.
The audience row deserves emphasis. Third-party wealth segments are modeled, and when checked against known customer files a large share of households in an "affluent" segment do not qualify. A publisher that knows its subscribers through registration and payment has firmer ground. A financial newspaper's logged-in subscribers, or an ad-supported streaming tier matched by household, give a higher hit rate than a probabilistic segment applied to anonymous traffic.
The Effective Cost Math: Which Is Actually Cheaper?
Combine the rates. The calculation below uses display, where the price gap is widest and the open exchange looks most attractive.
| Open exchange | Private marketplace | |
|---|---|---|
| Media CPM | $5.00 | $16.00 |
| Third-party audience data | $3.00 | $0 (publisher data in deal) |
| Total CPM | $8.00 | $16.00 |
| Viewable | 60% | 78% |
| In a suitable, legitimate environment | 85% | 99% |
| In the intended affluent audience | 18% | 45% |
| Qualified share of impressions | 9.2% | 34.7% |
| Cost per 1,000 qualified impressions | about $87 | about $46 |
Qualified share is the product of the three rates: 0.60 × 0.85 × 0.18 for the open exchange, and 0.78 × 0.99 × 0.45 for the private marketplace.
On these assumptions the private marketplace costs twice as much per impression served and about half as much per impression that counts. The result is sensitive to the audience rate. If the open exchange buy reached the intended audience 35 percent of the time, its qualified cost would fall to about $45 and the two would be level. This is why the comparison turns on audience size. An advertiser for whom half the population qualifies will find the open exchange efficient. An advertiser for whom 3 percent qualifies will not.
How to run this calculation on your own campaigns
- Take total cost including data and platform fees, by buying method.
- Pull measured viewability, or completion rate for video and CTV, from your verification vendor.
- Remove impressions on sites and apps outside your approved list.
- Estimate the on-target rate by matching exposed households to a customer or qualified-prospect file in a clean room, or by using a panel-based audience measurement.
- Divide cost by qualified impressions and compare.
Step four is the hard one and the one most often skipped. Without it, the comparison defaults to rate, and the cheaper line wins on paper.
Where the Open Exchange Still Earns a Place
The open exchange is a useful tool with a narrow set of jobs.
Retargeting known visitors. When the audience is defined by your own first-party data, the household is already qualified. The task is to find that person again at reasonable cost, and environment matters somewhat less. Even here, an inclusion list is worth keeping.
Broad reach for products with wide audiences. A premium product at an accessible price, where a third or more of adults could buy, loses less to audience mismatch.
Price discovery and testing. Running a small open exchange line against an inclusion list of the same publishers you buy through deals shows whether the deal floors are fair.
Filling gaps. Some good publishers do not offer deals at small budgets. An inclusion list of 50 to 300 hand-picked domains and apps bought in the open auction behaves much like a private marketplace at a lower rate, though without publisher data or priority.
The practice that separates acceptable open exchange buying from the kind the ANA measured is the inclusion list. Buying only from named sites and apps removes the long tail where made-for-advertising sites and misdeclared apps sit. An exclusion list, which blocks known bad sites and allows everything else, does not; new low-quality sites appear faster than they can be blocked.
Where Private Marketplaces Fall Short
A deal ID is not a certificate of quality, and private marketplaces bring their own problems.
- Low win rates. Deals often deliver a fraction of the forecast because of mismatched targeting, creative that has not been approved by the publisher, floors set above what the bidder will pay, or simple configuration errors. A new deal commonly needs one to two weeks of troubleshooting.
- Repackaged open inventory. Some deals offered by exchanges and intermediaries are the same impressions available in the open auction, bundled and marked up. Ask who the seller is and check it against the publisher's ads.txt file.
- Limited scale. A tightly targeted deal on one publisher may deliver tens of thousands of impressions a month. Reach requires a portfolio of deals, typically 10 to 30 for a national campaign.
- Frequency concentration. Fewer publishers and a small audience can push frequency high for the households that are reachable. Caps must be set across deals, and across platforms where possible.
- Minimums. Larger publishers and streaming services may require a spend commitment before issuing a deal.
- Curated deals vary. Multi-publisher packages assembled by a third party can be excellent or opaque. Request the domain and app list and the fee the curator takes.
A sound check is to ask for the win rate, the average clearing price against the floor, and the list of domains or apps actually delivered for every deal each month. Deals that clear far above floor are being overbid. Deals that deliver unfamiliar inventory need a conversation with the seller.
Connected TV: A Special Case
In streaming television the argument for private marketplaces is stronger than in display, for three reasons.
First, the price premium is smaller. Open exchange CTV at $15 to $28 against private deals at $30 to $55 is a gap of roughly two times, against three or four times in display.
Second, the quality gap is larger. Open exchange CTV supply includes a long tail of small apps, screensaver and pause-screen placements, and inventory resold through several intermediaries. Fraud schemes in CTV have typically worked by falsifying the app or device in the bid request, so that an impression declared as a major streaming service is something else. Buying from the service's own deal, with the seller verified as direct, closes most of that exposure.
Third, the largest services sell little or nothing in the open auction. Access to ad-supported tiers of Disney+, Netflix, Prime Video, Max, and Peacock comes mainly through direct and programmatic guaranteed arrangements and private deals. An open exchange CTV plan is, in practice, a plan that mostly excludes them.
For a luxury advertiser, our default is that 90 percent or more of CTV spend runs through private marketplace or guaranteed deals, with an inclusion list of named apps on anything else.
How Should You Split Budget Between Open Exchange and PMP?
Industry forecasters have reported for several years that private marketplace and direct programmatic spending in the US exceeds open exchange spending, and the open exchange share continues to decline. The right split for a given brand depends on audience size and price point.
| Advertiser profile | Qualified audience | Suggested PMP and direct share | Open exchange role |
|---|---|---|---|
| Luxury or high-consideration, purchase above $5,000 | Under 5% of households | 80% to 95% | Retargeting on an inclusion list |
| Premium, purchase $500 to $5,000 | 5% to 20% | 60% to 80% | Retargeting and curated reach |
| Accessible premium, under $500 | Over 20% | 40% to 60% | Reach and prospecting with strict lists |
Three working rules sit behind the table.
- The smaller the qualified audience, the higher the private share. Audience mismatch is the largest loss in the effective-cost calculation, and it grows as the audience narrows.
- The more the setting matters to the brand, the higher the private share. A $90,000 watch beside low-quality content loses something that a discount retailer does not.
- Never run the open exchange without an inclusion list. This single rule captures most of the available gain.
A transition plan for a brand that is mostly open exchange today
- Weeks 1 to 2: Export the full site and app list for the last 90 days. Rank by spend. Identify the 50 to 200 properties you would be content to show a client.
- Weeks 2 to 4: Convert open exchange lines to that inclusion list. Expect CPMs to rise 20 to 60 percent and delivered impressions to fall.
- Weeks 3 to 8: Negotiate deals with the top 10 to 20 publishers and streaming services on the list. Request publisher audience data where it exists.
- Weeks 6 to 12: Shift budget as deals begin delivering. Review win rates and clearing prices every two weeks.
- Quarter 2: Measure with a holdout group. Compare cost per qualified visit and cost per incremental conversion before and after, and do not judge the change by average CPM.
Total impressions will fall, often by half or more. That is the intended result. Reports should be redesigned around qualified reach and incremental outcomes beforehand, so that nobody reads the lower impression count as a decline in performance.
Common Mistakes
- Comparing on CPM alone.
- Assuming every deal ID means premium inventory without checking the seller and the delivered placements.
- Launching deals and not troubleshooting them, then concluding that private marketplaces do not scale.
- Relying on exclusion lists in the open exchange.
- Layering third-party data on top of a deal that already includes publisher data, paying twice for targeting and shrinking delivery.
- Setting frequency caps per deal and ending up with 30 exposures a week to the same household across ten deals.
- Reporting impressions as the headline number after a shift that is designed to reduce them.
How Stillwater Media Buys
For the brands we work with, where a customer is worth more than $5,000 and the decision takes longer than 30 days, the large majority of spend runs through private marketplace and guaranteed deals negotiated with named publishers and streaming services. Open exchange buying is limited to inclusion lists and mainly to retargeting. We report win rate, clearing price, and delivered placements for every deal, itemize platform and data fees, and measure outcomes with holdout tests so the comparison is made on incremental results.
We take on a limited number of engagements each quarter. If you want to know what your current programmatic budget is buying, and what it would buy under a different structure, apply to work with Stillwater Media.
About Stillwater Media
Stillwater Media is a selective performance media agency for luxury and high-consideration brands. We plan and buy premium CTV on services including Disney+, Netflix, and Prime Video, along with programmatic video and display, digital out-of-home, streaming audio, YouTube Select, podcasts, native, and social, using private marketplace deals, affluent audience engineering, and incrementality testing. We work with brands in private aviation, luxury real estate, wealth management, private clubs, luxury automotive, premium DTC, and luxury hospitality. Signal. Strategy. Scale.
Frequently Asked Questions
What is the difference between open exchange and private marketplace programmatic?
In the open exchange, any advertiser can bid on a publisher's impressions in a public auction, usually without knowing the publisher in advance. In a private marketplace, a publisher invites selected buyers to bid on specified inventory under a deal ID with a negotiated price floor, and those buyers get priority over the open auction.
Is a private marketplace more expensive than the open exchange?
Per impression, yes: private marketplace CPMs typically run 1.5 to 4 times open exchange rates depending on format. Per qualified impression the result often reverses, because private deals have higher viewability, almost no low-quality sites, and a higher share of the intended audience.
When should an advertiser use the open exchange?
The open exchange suits retargeting people already identified through first-party data, broad-reach campaigns for products with large audiences, and price testing. It should be bought against an inclusion list of named sites and apps, never across all available inventory.
Are private marketplace deals always premium inventory?
No. Some deals repackage inventory that is also available in the open auction, and some multi-publisher packages are opaque about what they contain. Buyers should confirm the seller against the publisher's ads.txt file and review the placements each deal actually delivered.
How much of a luxury brand's programmatic budget should go to private marketplaces?
For brands with purchase values above $5,000 and qualified audiences under 5 percent of households, a reasonable target is 80 to 95 percent in private marketplace and direct deals. The remainder is best limited to retargeting on a hand-picked inclusion list.
