Performance Max and Search campaigns both appear in Google Search results, which creates a frequently misunderstood overlap problem. Google's official guidance states that Search campaigns take priority over PMAX in the same auction when they both match a query — but this priority is conditional, and the interactions between the two campaign types are more nuanced than the documentation implies. Getting the co-existence right is one of the most consequential structural decisions for accounts running both.
How the auction priority rule actually works. If a Search campaign has a keyword that matches the user's query, the Search campaign takes priority over PMAX for that auction. This only applies when the Search campaign has an eligible matching keyword. If PMAX runs in an account with gaps in Search keyword coverage, PMAX fills those gaps. This is often the intended behavior — PMAX is designed to capture demand that keyword-based campaigns miss, not to compete with them on covered terms.
The cannibalization scenario. Cannibalization happens when PMAX serves on queries already covered efficiently by Search campaigns. If PMAX serves on branded queries, exact match terms, or high-value Search terms your Search campaigns already handle at acceptable CPA, PMAX inflates its apparent performance by claiming conversions from easy queries while consuming budget that could drive incremental reach elsewhere. This happens most often when PMAX is added without brand exclusions or without tight Search keyword coverage.
Brand query exclusions in PMAX. PMAX does not support negative keywords through the standard interface — you cannot add terms the same way you would in Search. Brand exclusions can be applied at the account level via Google support. Campaign-level negative keyword lists can also be applied to PMAX in some configurations. Branded query protection is the most critical PMAX exclusion: branded queries served through PMAX instead of a dedicated brand Search campaign typically produce higher branded CPCs with less campaign control.
Using Search Term Insights from PMAX. PMAX provides Search Terms Insights — a categorized summary of query themes that drove conversions, not the full query report Search provides. Reviewing this data shows where PMAX is serving and which query categories drive results. If the insights show heavy coverage of your exact Search keywords, the campaigns need structural adjustment. If PMAX insights show query categories not covered by Search, that's healthy incremental coverage working as intended.
The optimal structural relationship. The most efficient structure for accounts running both: Search campaigns cover all high-intent, well-understood query categories with tight keyword coverage and complete negative keyword lists. PMAX handles non-search inventory (Display, YouTube, Discover, Gmail) and long-tail or undefined query coverage that Search keywords don't reach. This uses PMAX for its strengths — multi-channel, AI-first optimization, novel query discovery — without creating Search/PMAX conflict on core terms.
Asset quality determines PMAX delivery. PMAX performance is heavily influenced by asset quality. Google's Asset Group quality indicators (Good, Low, Poor) reflect how well your creative assets and text variations work together. Low-quality Asset Groups suppress delivery in competitive inventory. For accounts transitioning from Search to PMAX, the asset creation step is consistently underinvested — importing Search ad copy directly into PMAX text assets without adapting it to the multi-channel context produces poor Asset Group quality.
PMAX after Smart Shopping migration. Accounts that previously ran Smart Shopping campaigns had them automatically migrated to PMAX. Comparing post-migration PMAX performance directly to pre-migration Smart Shopping is valid for the first 90 days, but PMAX counts multi-channel conversions (Display, YouTube view-throughs) that Smart Shopping did not. Evaluate on total CPA with attribution context rather than platform-reported ROAS alone to avoid over- or under-crediting PMAX.
Reporting limitations and operational implications. PMAX provides less transparency than Search: no keyword-level performance data (only theme-level insights), no self-serve placement exclusions for Display and YouTube, and limited audience performance segmentation. If your optimization process requires keyword-level data to make bid decisions or placement-level exclusions to control brand safety, PMAX's reporting gaps are real operational constraints that need workflow accommodation.
Digital Face analyzes the overlap between your PMAX and Search campaigns, identifies query categories where cannibalization may be occurring based on PMAX insights versus Search keyword coverage, and flags Asset Group quality issues that limit PMAX delivery. Free plan at digital-face.nl, no credit card required.