Can you run two ad networks at once? What 38,000 sites actually do

The question comes up constantly, usually phrased as an optimisation: if one network pays for some impressions and another pays better for others, why not run both and take the higher bid every time?

There are good technical answers about header bidding and how managed networks already do this internally. But the more useful answer is empirical — we can see what live publishers chose.

The distribution

Why almost nobody stacks

Three forces push in the same direction, and they compound.

• Exclusivity. The large managed networks require it. That is the whole contract: they take over your ad stack, so running a competitor alongside is not an optimisation, it is a breach.
• They already do the auction. A managed network’s value is running many demand sources against each other on your behalf. Adding a second network on top duplicates that layer rather than extending it, and the two compete for the same impressions with worse information than either has alone.
• Performance cost. Two ad stacks means two sets of scripts, two consent integrations and roughly double the layout instability. The revenue gain has to beat the traffic loss from a slower page, and usually does not.

The combinations that do occur

The exceptions are not random. These are the network pairs we find on the same site most often:

Read that table and the pattern is legible. Most entries are one display network next to a specialist that sells a format the first does not — video alongside display, or a gaming specialist alongside a generalist. That is complementary inventory, not two networks fighting over the same ad slot.

The other cluster is migration: two large competing networks appearing together because a publisher moved and the old seller file has not caught up. We looked at the clearest case of that in sites running both Mediavine and Raptive.

So should you?

If you are on a managed network, check your contract before anything else — the answer is probably no, and the downside is losing the network rather than a percentage of revenue.

If you are self-managing, the honest framing is that adding a second display network is rarely where the gain is. The publishers in the pairs table above are mostly adding a format they did not have, not a second bidder for the same slot. That is the version of stacking the data supports.

You can check any specific site’s full network list — including sites that carry several — by searching it from the home page.

What header bidding actually changed

The instinct behind the question is sound, and the industry acted on it a decade ago — just not in the way publishers imagine. Header bidding lets many demand sources bid on the same impression simultaneously before the ad server decides, which is precisely the “take the higher bid every time” mechanism people have in mind.

The point is that this happens inside a managed network, not between two of them. When you join one, you are buying its header bidding configuration and its demand relationships. Adding a second managed network on top does not create a bigger auction; it creates two auctions that cannot see each other, each with less inventory to work with, and the ad server has to pick between two winners chosen on incomplete information.

That is why the distribution above looks the way it does. Stacking is not forbidden because it would work too well — it mostly does not work.

When a second partner does make sense

• A different format. Video, native or audio sold by a specialist alongside a display partner. This is the largest legitimate group in the pairs table.
• A different geography. A network with strong demand in a region your main partner sells poorly, applied to that traffic only.
• A different property. Separate domains under one publisher, each with its own partner. Common, and it accounts for some of the pairs above.
• A transition. Overlapping for a short window while you move — the honest version of stacking, and temporary by design.

What is not on that list is running two display networks against each other on the same ad slots on the same pages. That is the version of the idea people usually mean, and the one the data gives no support to.

Every figure on this page is read from our own index when the page is built, and refreshes on a weekly cycle — so the numbers move as the data does. Method and evidence rules: coverage & method.