Performance Max and CSS - What You Need to Know

Performance Max has become the dominant campaign type for e-commerce advertisers, combining Shopping, Search, Display, YouTube, Discover, and Gmail into a single automated campaign. The CSS advantage applies to the Shopping component of PMax, and understanding how it works is essential for any advertiser running PMax in the EEA, UK, or Switzerland.

What Is Performance Max?

Performance Max (PMax) is Google's AI-driven campaign type that serves ads across all Google-owned channels from a single campaign. Launched in late 2021 and expanded through 2022 and 2023, PMax replaced Smart Shopping campaigns and has since become the default recommendation for e-commerce advertisers.

Unlike standard Shopping campaigns, where you control product groups, bids, and networks directly, PMax uses machine learning to make most optimization decisions. You provide the campaign with goals (conversions or conversion value), budget, product feed, creative assets, and audience signals. Google's algorithm then determines where, when, and how to show your ads to maximize performance against your goals.

For e-commerce, the Shopping component of PMax is typically the largest driver of performance. PMax serves Shopping ads on the Google Search results page and the Shopping tab using product data from your Merchant Center feed. These Shopping placements participate in the same auction as standard Shopping campaigns and are subject to the same CSS economics.

Key Differences from Standard Shopping

• Multi-channel: PMax serves across Shopping, Search, Display, YouTube, Discover, and Gmail simultaneously. Standard Shopping is limited to the Shopping auction.
• Automated bidding only: PMax requires automated bidding (Maximize Conversions or Maximize Conversion Value, optionally with a target ROAS). Manual CPC is not available.
• Asset groups instead of ad groups: PMax uses asset groups that contain images, text, videos, and audience signals. The Shopping component pulls product data directly from the feed.
• Limited search term visibility: PMax provides less transparency into which search terms triggered your ads compared to standard Shopping campaigns.
• No negative keywords (limited): Google has gradually added some negative keyword support for PMax, but it remains more restricted than standard Shopping.

How CSS Benefits the Shopping Component

The mechanics of CSS in PMax are identical to standard Shopping campaigns. When your Merchant Center is associated with an independent CSS partner like Cobiro, the Google Shopping Europe margin is removed from the Shopping auction for your products. This applies to every Shopping impression served by PMax, whether it appears on the main Search results page or the Shopping tab.

Because PMax uses automated bidding, the algorithm detects the improved auction efficiency and adjusts its behavior accordingly. In practice, this means one of two outcomes (or a combination of both):

• More Shopping impressions and clicks for the same budget: The algorithm recognizes that Shopping placements have become more cost-efficient and allocates more budget toward them.
• Lower overall cost for the same volume of conversions: If the campaign is target-ROAS constrained, the algorithm maintains the same conversion volume while spending less.

The net effect is the same as with standard Shopping: approximately 20% better economics on every Shopping click. The difference with PMax is that the savings are blended with non-Shopping placements, so the headline CPC reduction across the entire PMax campaign may appear smaller than 20% when viewed in aggregate.

How to Verify CSS Is Active on PMax

Because PMax does not have a CSS column in reporting, verifying that your CSS partner is active requires checking outside of Google Ads.

Method 1: Merchant Center Settings

The most reliable method. In Google Merchant Center, navigate to Settings and then Shopping ads. Under the CSS section, you will see which CSS partner is associated with your account. If it shows your CSS partner (for example, Cobiro), the association is active and applies to all Shopping placements, including those served by PMax.

Method 2: Search for Your Products

Search for one of your products on Google from an EEA country. Find your Shopping ad in the results. Below the ad, you should see an annotation reading "Ads by Cobiro" (or your CSS partner's name). This annotation confirms that the ad was submitted through your CSS partner rather than through Google Shopping Europe.

Method 3: Google Ads Campaign Report

While PMax does not show a CSS column, you can check the Insights tab or the Products tab within your PMax campaign to confirm products are active and being served. Cross-reference this with the Merchant Center CSS setting to confirm the association.

Method 4: Third-Party Tools

Tools such as PMax Insights (originally developed by Producthero, now part of Channable) can break down PMax performance by channel, showing you how much spend and how many clicks come from the Shopping component versus other placements. This helps you quantify the CSS impact within your PMax campaigns. BigShopper's Benchmark Insights tool can also show your CSS association status and compare your Shopping performance against competitors.

Asset Groups and Product Feed Integration

PMax campaigns use asset groups to organize creative elements and targeting. Each asset group contains text assets (headlines, descriptions), image assets, video assets (optional, though Google will auto-generate if none are provided), audience signals, and a product feed connection.

For e-commerce PMax, the product feed is the most important element. The Shopping component of PMax pulls directly from your Merchant Center feed, just like standard Shopping campaigns. This means that all the feed optimization principles covered in the Feed Optimization guide apply equally to PMax.

Structuring Asset Groups

Google recommends creating separate asset groups for distinct product categories or themes. Each asset group can target a specific subset of your product feed using listing groups (the PMax equivalent of product groups in standard Shopping). This allows you to:

• Write category-specific ad copy that aligns with the products being shown
• Use category-appropriate images and videos
• Apply different audience signals to different product segments
• Monitor performance at the asset group level to identify underperforming segments

For large catalogs, creating too many asset groups can fragment data and slow the learning process. A common approach is to create one asset group per major product category, with a catch-all asset group for smaller categories. This balances specificity with data volume.

PMax Reporting Limitations

One of the most common frustrations with PMax is limited reporting transparency. Understanding these limitations helps you set realistic expectations and identify the right tools for deeper analysis.

• No search term report: PMax provides search term insights but not a full search term report like standard Shopping campaigns. You can see search term categories and themes, but not individual query-level data for all queries.
• No network-level bidding control: You cannot set separate bids for Shopping vs. Display vs. YouTube. Google's algorithm allocates budget across networks automatically.
• Limited placement reporting: While you can see some placement data, it is aggregated and does not provide the same granularity as Display or Video campaigns.
• No CSS column: Unlike standard Shopping campaigns, PMax does not show a CSS column in reporting. You must verify CSS status through Merchant Center.

Google has been gradually improving PMax reporting since its launch. Recent additions include better asset performance ratings, more granular search term insights, and improved audience reporting. However, PMax remains less transparent than standard Shopping for advertisers who want query-level control.

PMax Optimization Tips for CSS Users

Once your CSS association is active with a provider like Cobiro, these optimization tips will help you maximize the benefit within PMax:

1. Prioritize Feed Quality

Because PMax relies heavily on the product feed for Shopping placements, feed quality has an outsized impact. Invest in product title optimization, complete attribute coverage, and high-quality images. A well-optimized feed combined with CSS gives you both better auction economics and better query matching.

2. Use Audience Signals Strategically

Audience signals help PMax identify high-value users faster. Add your remarketing lists, customer match lists, and relevant in-market and affinity audiences. These signals are not hard targets; they are hints that guide the algorithm's initial learning phase.

3. Set Realistic ROAS Targets

If using Target ROAS, start with a target that is achievable based on your historical performance. After switching CSS, you may be able to increase your target ROAS by 15 to 20% over the following weeks as the improved auction economics take effect. Increase the target gradually to avoid disrupting the algorithm. For more on bidding approaches, see Bidding Strategies.

4. Segment with Listing Groups

Use listing groups to exclude low-margin or poorly-performing products from specific asset groups. This gives you some of the product-level control that PMax otherwise removes. Combine this with custom labels for maximum flexibility.

5. Monitor the Shopping Share

Use third-party tools to estimate what percentage of your PMax spend goes to Shopping placements. If Shopping accounts for 70% of spend, the CSS advantage drives a significant portion of your campaign economics. If Shopping is only 30%, the blended CSS impact is smaller, and you should focus optimization efforts on the non-Shopping components as well.