Is Google Prioritising Performance Max Over Search Campaigns?
Performance Max campaigns have been one of the most debated features in Google Ads over the last few years. Some advertisers believe they unlock incremental growth across Google’s entire ecosystem, while others argue they simply cannibalise existing Search campaign performance.
In a recent client case study, an interesting scenario emerged that challenged conventional wisdom around campaign cannibalisation. The results raised an important question:
Is Google actively favouring Performance Max over standard Search campaigns?
Let’s break down what happened, what was tested, and what the findings could mean for advertisers running both campaign types simultaneously.
Understanding the Difference Between Search and Performance Max
Before diving into the experiment, it’s important to understand how these two campaign types operate.
Search Campaigns
Search campaigns are straightforward. Your ads appear directly on Google Search results pages when users search for relevant keywords.
You control:
- Keywords
- Match types
- Ad copy
- Bidding strategy
- Budget allocation
Search campaigns are highly transparent and typically easier to optimise manually.
Performance Max Campaigns
Performance Max (PMax) is very different.
Instead of focusing only on Google Search, PMax distributes ads across Google’s entire inventory, including:
- Google Search
- YouTube
- Display Network
- Gmail
- Google Discover
- Shopping placements
- Android app inventory
The campaign operates largely as a “black box”, where Google automates placements, bidding, and audience targeting based on the goals you set.
The Cannibalisation Debate
One of the biggest concerns advertisers have with Performance Max is cannibalisation.
Here’s the logic behind the concern:
- A Google Ads account can only show one ad per auction
- If both a Search campaign and a Performance Max campaign are eligible for the same search query, Google chooses one based on ad rank
- That means PMax could potentially “steal” traffic that would otherwise go to Search campaigns
Conventional wisdom suggests that if you remove Performance Max, the Search campaign should absorb most of those impressions and conversions instead.
But in this particular case, that’s not what happened.
The Client Scenario
The account in question was running:
- A high-performing Search campaign
- A Performance Max campaign
- Both targeting the same CPA goal of £30
The Search campaign had:
- Excellent Quality Scores (mostly 10/10)
- Plenty of available budget
- Strong ad rank potential
- Only around 25% impression share
That last point is important.
A 25% impression share means the account was missing roughly 75% of eligible searches. In theory, there was significant room for the Search campaign to grow further.
Meanwhile, the Performance Max campaign was scaling aggressively and generating a large volume of additional conversions.
When the data was analysed more closely, something even more interesting appeared:
Most of the Performance Max conversions were actually coming from Search inventory.
This raised a critical question:
Why wasn’t the standard Search campaign capturing those conversions already?
The Initial Theory
At first glance, the explanation seemed simple.
Perhaps the Search campaign’s CPA target was restricting its ability to compete aggressively in auctions.
If the Search campaign had lower ad rank because of bidding limitations, then Performance Max might simply be winning more auctions.
That would make sense logically.
However, there was a major complication:
- Both campaigns had the same £30 CPA target
- The Search campaign still had unused budget
- Quality Scores were extremely strong
So why was Performance Max scaling while Search remained relatively static?
The Experiment
To test the theory, a controlled experiment was run.
The Performance Max campaign’s target CPA was reduced significantly:
- From £30
- Down to £20
This dramatically restricted Performance Max bidding capability.
As expected:
- PMax volume dropped
- The campaign became less aggressive
- Conversions decreased
But here’s the surprising part:
The Search campaign did not increase its performance at all.
No meaningful increase in:
- Impressions
- Clicks
- Leads
- Spend
The Search campaign essentially remained flat.
Why This Result Matters
This outcome contradicts the common assumption about cannibalisation.
If Performance Max was simply taking traffic away from Search, then weakening PMax should have allowed Search to reclaim at least some of that traffic.
Even a small uplift would have supported the theory.
Instead:
- Performance Max lost volume
- Search did not gain volume
That suggests the incremental conversions generated by PMax were not being directly transferred from the Search campaign.
What Could Be Happening?
There are several possible explanations.
1. Google Is Favouring Performance Max
This is the most controversial interpretation.
The evidence suggests that Google may be prioritising Performance Max campaigns in auctions, even when Search campaigns are equally capable of serving ads.
In this scenario:
- Search campaigns are not fully participating in all eligible auctions
- Performance Max is being given preferential access
- Google’s automation may internally prioritise PMax inventory allocation
This would explain why reducing PMax bidding power did not benefit Search.
2. Performance Max Uses Additional Signals
Another possibility is that Performance Max has access to richer machine learning signals than standard Search campaigns.
For example:
- Cross-channel behavioural data
- Audience intent modelling
- YouTube engagement signals
- Shopping behaviour
- Automated creative combinations
These additional signals could allow PMax to identify and enter auctions the Search campaign simply does not compete in effectively.
3. Search Campaigns Are More Constrained Than Advertisers Realise
Even with excellent Quality Scores and available budget, Search campaigns may still face hidden limitations caused by:
- Smart bidding models
- Query matching thresholds
- Auction-time prediction systems
- Conservative CPA bidding behaviour
Meanwhile, Performance Max may have greater flexibility to stretch beyond those constraints.
The Bigger Issue With Performance Max Transparency
One of the frustrations advertisers continue to face is the lack of transparency inside Performance Max campaigns.
Unlike Search campaigns, advertisers cannot fully see:
- Exact keyword targeting
- Search query behaviour
- Placement-level performance
- Auction dynamics
This makes diagnosing incremental performance extremely difficult.
In this case, the advertiser could see that most conversions originated from Search-related traffic, but there was no definitive explanation for why Search campaigns themselves failed to absorb that demand.
When Performance Max Truly Cannibalises Search
It’s important to note that this case was unusual.
In many accounts, advertisers absolutely do see cannibalisation.
Typical signs include:
- Search campaign conversions decline after launching PMax
- Combined conversions stay roughly the same
- Overall spend increases
- Search impression share drops
In those situations, Performance Max may simply be redistributing existing demand rather than creating new demand.
This particular case stood out because:
- Total conversions genuinely increased
- Search did not decline significantly
- Search still had room to scale
- Yet PMax captured most of the growth
That combination is what made the results so interesting.
What Advertisers Should Do
If you are running both Search and Performance Max campaigns, there are several practical steps worth taking.
Monitor Search Impression Share
Low impression share may indicate growth opportunity within Search campaigns themselves.
Check:
- Lost IS due to rank
- Lost IS due to budget
- Auction competitiveness
Compare Search Query Behaviour
Where possible, compare:
- Brand vs non-brand performance
- Incremental search terms
- Conversion quality
- Assisted conversions
This can help identify whether PMax is genuinely expanding reach.
Test CPA Targets Carefully
As demonstrated in this experiment, changing CPA targets can reveal how campaigns interact with each other.
Watch for:
- Traffic migration
- Impression changes
- Conversion redistribution
Don’t Assume Incrementality
Just because Performance Max reports additional conversions does not automatically mean they are incremental.
Always test:
- Holdout periods
- Budget shifts
- Controlled experiments
Final Thoughts
This case study highlights just how complex Google Ads has become in the automation era.
The traditional assumption that Search campaigns should absorb Performance Max traffic when PMax weakens did not hold true in this scenario.
Instead, the results suggested one of two possibilities:
- Performance Max has access to advantages Search campaigns do not
- Google may actively prioritise Performance Max inventory delivery
Neither explanation is especially comforting for advertisers who value transparency and control.
What is clear, however, is that advertisers can no longer assume Search and Performance Max behave as interchangeable traffic sources.
The relationship between the two campaign types appears far more nuanced — and possibly more biased — than many originally thought.
