The data: US retail media ad impressions declined 18.9% YoY to 107.4 billion in Q2 2026, per Sensor Tower’s “Retail Media Report 2026,” and 17% between H1 2025 and H1 2026.

• Amazon remained the dominant platform with a 60% share of the retail media market, though its 16% YoY drop in ad impressions contributed to the broader market decline.
• Home improvement retailers—specifically Home Depot and Lowe’s—stood out as the top retail media network (RMN) growth drivers in Q2 2026.

Sensor Tower’s report highlights how retailers are taking different approaches to position their inventories.

Zooming in on off-site: Retailers are following shoppers beyond their own digital storefronts with off-site media.

• Vertical networks Instacart and Sephora kept 100% of their campaigns off-site in H1 2026.
• Best Buy increased its off-site share to 93.2%, up 17.2 percentage points YoY from H1 2025.
• Target grew off-site share to 91.5%, up 7.5 points.

Instacart’s and Sephora’s use of off-site inventory to chase user attention outside owned apps trades purchase-intent certainty for reach. Meanwhile, Best Buy and Target are extending brand consideration campaigns to audiences that aren’t actively shopping on-site.

Zooming in on on-site: Campaign priorities diverged for the two RMNs with the largest impression share—Amazon and Walmart.

• 56.1% of Amazon’s impressions share was on-site in H1 2026—more than any other company but down 7.4% YoY.
• Walmart boosted its on-site impressions 170.7% YoY, pushing its on-site share to 42.5%. The company has also been expanding its ad tools for third-party advertisers.

Amazon and Walmart are able to focus on owned inventory because their size already offers both reach and intent inside a single environment. The combination of Amazon’s shrinking impression volume and dominating market share shows how advertisers are still pushing dollars there, which could increase CPMs.

Recommendations for marketers: The retail media market is changing where and how ads appear. Marketers should treat divergence in funnel as a guide for budget allocation, led by campaign goals.

• Reserve placements on Amazon or Walmart for times when in-the-moment purchases and conversions are the goal.
• Use vertical networks like Instacart, Sephora, Best Buy, and Target to support awareness efforts when reach is the main priority.
• Track the growth of players like Home Depot and Lowe’s to see whether home improvement retailers continue as a major pillar of retail media.