The Maze: Retailers can sell advertising that appears beyond their own shopping sites and apps. A brand buys through the retailer's advertising network, but reaches people elsewhere online. That is off-site retail media. EMARKETER's 2027 forecast gives Amazon and Walmart a combined 81% of US spending in this category. Advertising can spread across more places while the money still flows through very few buying routes.
Two retailers are forecast to take roughly four dollars in five. Amazon and Walmart's combined 81% leaves 19% for every other network together, calculated as 100% minus 81%. This measures their share of US off-site retail media spending in 2027. It does not measure their share of all online advertising or all retail media. The individual Amazon and Walmart shares are hidden in the available evidence, so the finding is about their combined weight. It cannot establish which company leads, or how close the two are.
Off-site changes where an ad appears, not necessarily who sells it. An ad on a retailer's own shopping site reaches people already visiting that store. An off-site ad is bought through the retailer's network or buying service and appears elsewhere. The source's examples include Amazon's advertising buying platform and Etsy Offsite Ads. This distinction matters for brands seeking reach beyond a store's visitors: expanding the range of places where ads appear does not automatically expand the range of businesses through which they buy them. More destinations can still sit behind a concentrated set of buying relationships.
Scale could make the largest networks harder to leave. If brands already allocate most off-site spending to two retailers, those retailers can become central to campaign planning. A brand may find it simpler to expand an existing buying relationship than add another network, reporting process and budget decision. EMARKETER's public report outline highlights simpler Amazon buying and Walmart integrations and self-service tools. Those are plausible ways to reduce that friction. The forecast does not prove that convenience caused the concentration, or that the largest networks deliver better returns. It identifies the scale at which those competitive advantages could matter.
The remaining 19% is a differentiation problem, not proof of a worthless market. A spending share alone says nothing about the dollar size or profitability of that remainder. Smaller networks therefore need a reason for brands to add them: for example, access to shoppers or useful advertising opportunities that existing campaigns do not already cover. That is a strategic implication of the forecast, not a measured result. Competing solely as another place to buy similar reach could be difficult when two retailers already account for most projected spending. A distinctive audience or a simpler buying process still has to earn its place in the budget.
Why it matters: Retailers taking their advertising off-site can compete for budgets beyond the ads shown in their stores. Yet this forecast suggests that the US opportunity could reinforce two large intermediaries rather than distribute spending evenly across retail networks. For brands, a wider advertising footprint and a wider choice of buying partners are separate questions. For smaller retailers, launching an ad network is only the opening move; they must give advertisers a reason to add another relationship.
Sources: EMARKETER: US Retail Media Ad Spending Forecast H2 2026, Arielle Feger, October 28, 2026; Arielle Feger's source post. The finding uses EMARKETER's August 2026 forecast, not realized spending.
