Retail Media Networks Explained: Amazon vs Walmart vs Instacart

Retail media networks are the fastest-growing line item in most brand budgets, and also the least understood. Here are retail media networks explained in plain terms: a retailer takes the purchase data it already collects, opens up ad inventory against it, and reports back exactly which ads led to which sales. That closed loop is why US advertisers are on track to spend roughly $71 billion on retail media in 2026 — about 18% growth year over year, and close to 30% of all US digital ad spend, according to eMarketer forecasts.

The problem is that "retail media" now covers three very different things, sold by dozens of retailers, at wildly different price floors. This guide breaks down what you are actually buying, then compares the three networks most brands evaluate first: Amazon Ads, Walmart Connect, and Instacart.

What a retail media network actually is

A retail media network (RMN) is a retailer's in-house ad business. The retailer sells access to two assets: its shopper audience, and its transaction data.

The transaction data is the part that matters. When a shopper sees your sponsored listing and buys the product two hours later, the retailer knows — because the impression and the purchase happen inside the same logged-in account. No modelled conversion, no cross-device guesswork, no third-party cookie. That is what people mean by "closed-loop measurement," and it is a meaningfully cleaner signal than most of what you will find in standard attribution models.

The trade-off: the retailer grades its own homework. Every RMN reports on its own inventory, with its own attribution windows, and none of them talk to each other.

The three surfaces: onsite, offsite, and in-store

Onsite is inventory on the retailer's own properties — sponsored product listings in search results, banners on category pages, placements in the mobile app. This is where the intent is highest and where most brands start. It behaves like paid search: keyword-driven, auction-based, measured on ROAS and ad-attributed sales.

Offsite is retailer data activated somewhere else — programmatic display, connected TV, social. You are buying the retailer's audience, not the retailer's page. US offsite retail media spend is forecast to top $17 billion in 2026, up roughly 29.5%, per eMarketer. Offsite is where retail media stops being a shelf tactic and starts being a full-funnel channel, and it typically runs through a demand-side platform rather than a self-serve console.

In-store is the newest surface: digital end caps, checkout screens, smart coolers, in-store audio, and app-assisted shopping. It has been messy to measure, which is why the IAB and IAB Europe published final In-Store Retail Media Definitions and Measurement Standards — a shared vocabulary that splits the store into five zones (exterior, entrance, in-aisle, checkout, and other perimeter areas). Retailers have until the end of July 2026 to move onto the updated version. If you buy in-store, ask your rep which standard their reporting follows.

Amazon Ads: the default, for better and worse

Amazon is not one of the retail media options. It is most of the market. Analysts put Amazon at roughly three-quarters of US retail media spend, and its ad business cleared $17.2 billion in Q1 2026 alone, up about 22% year over year, with trailing-twelve-month revenue past $70 billion.

What you get: unmatched scale, the deepest set of ad formats (sponsored products, brands, display, video, Amazon DSP, plus Prime Video and Twitch inventory), and a genuinely mature reporting stack. Amazon has also pushed AI creative tooling hard through 2026, which lowers the production cost of testing variants.

What you pay for it: the most competitive auction in retail media. Amazon CPCs have climbed steadily, and in crowded categories a large share of spend goes to defending your own branded terms against competitors bidding on them. Amazon is also the least flexible partner on data — you can measure inside the walled garden, but pulling granular data out for your own modelling is limited.

Best fit: brands where Amazon is already a top-three sales channel, or brands that need reach at a scale no other RMN can deliver.

Walmart Connect: the fastest-growing challenger

Walmart Connect is the clearest number-two, and it is growing faster than the market. Walmart's global advertising business grew 37% in its most recent quarter, with US Walmart Connect up 44% excluding VIZIO, on a base of roughly $6.4 billion in annual advertising revenue.

Two things make Walmart worth a serious look. First, the auction is less saturated than Amazon's, so cost-per-click is generally lower for comparable placements — the arbitrage will not last forever, but it exists today. Second, Walmart has moved aggressively on offsite. Its VIZIO acquisition gave it an owned CTV platform, and in 2026 it opened Walmart first-party data to additional DSPs and supply partners, including Yahoo's DSP with VIZIO inventory via Magnite. That means you can now activate Walmart shopper data outside the Walmart DSP — a real change for brands running connected TV campaigns who want purchase-based targeting rather than demographic proxies.

Walmart also reaches a different shopper: more in-store, more value-oriented, broader geographic spread than Amazon's Prime-heavy base.

Best fit: CPG, grocery, household and mass-market brands with real shelf presence at Walmart, and any brand that wants retail data feeding its CTV buy.

Instacart: narrow reach, exceptional intent

Instacart is smaller — advertising and other revenue crossed $1 billion for the first time in 2025, with Q1 2026 at $286 million, up 16% year over year. But the audience quality is the argument. Someone on Instacart is filling a basket right now. There is almost no top-of-funnel browsing to pay for.

Instacart also punches above its own storefront through Carrot Ads, its white-label technology powering retail media for 240+ retail partners including Sprouts, Schnucks and Hy-Vee, reaching thousands of CPG advertisers. Buying Instacart increasingly means buying a network of regional grocers, not just one app.

The limits are real: it is grocery and grocery-adjacent, basket sizes are modest, and available impression volume caps out quickly for large budgets.

Best fit: food, beverage, personal care and household brands that want incremental sales without cannibalizing Amazon spend. For platform-level performance figures, see our 2026 retail media benchmarks breakdown.

Amazon vs Walmart vs Instacart at a glance

How to choose without guessing

Skip the platform question first. Answer these four in order.

1. Where does the product already sell? Retail media amplifies existing distribution; it does not create it. If you do not have strong shelf or listing presence at a retailer, ads there will underperform regardless of creative.

2. What is the job — defence or discovery? Defending share on branded terms is cheap and high-ROAS but rarely incremental. Winning unbranded category searches costs more and moves the business. Budget them separately or the blended number will lie to you.

3. Can you afford the entry point? Self-serve sponsored formats on all three platforms open at effectively any budget. Managed service and DSP-bought offsite inventory generally require committed spend in the tens of thousands per quarter. Do not stretch into DSP before onsite is optimized.

4. How will you measure incrementality? Every RMN reports flattering, non-comparable numbers. Holdout tests and geo experiments — the kind of work covered in our paid media services — are the only way to know what retail media added versus what you would have sold anyway.

What retail media does not solve

Retail media is a conversion channel wearing a full-funnel costume. It captures demand efficiently; it creates very little. Brands that shift the entire budget into RMNs typically see ROAS look excellent for two quarters, then watch unbranded search volume and category share slowly erode.

Treat it as one layer inside a cross-channel plan, alongside programmatic display and CTV for reach and your own first-party data strategy for durable audience targeting you actually control. The retailer's data is rented, not owned.

Frequently asked questions

What is a retail media network in simple terms?

It is a retailer selling ad space against its own shopper data. You buy placements on the retailer's site, app, off-platform inventory, or in-store screens, and the retailer reports which ads drove which purchases using its own transaction records.

Is retail media only for CPG and grocery brands?

No. CPG dominates because grocery retailers built the first networks, but electronics, apparel, home, auto parts, pharmacy and even financial services now run retail media through networks like Amazon, Best Buy, Target and Lowe's. If a retailer sells your category, it likely has an ad business.

How much do I need to spend to start?

Sponsored product formats on Amazon, Walmart Connect and Instacart are self-serve with effectively no minimum — you can test with a few hundred dollars a month. Managed-service programs and DSP-bought offsite inventory are where meaningful commitments begin, typically in the tens of thousands per quarter.

Should I run all three networks at once?

Rarely, at the start. Pick the retailer where your sales are strongest, get onsite performance stable and profitable, then expand. Running three under-funded programs produces three inconclusive datasets.

Can I compare ROAS across Amazon, Walmart and Instacart directly?

Not reliably. Each network uses different attribution windows and definitions of an ad-attributed sale, so the raw numbers are not like-for-like. Compare each platform to its own trend line, and use incrementality testing for cross-platform decisions.

Next step

Retail media rewards brands that pick deliberately and measure honestly, and punishes brands that spread thin across every network with a rep who called them.

If you want a second opinion on where your retail media budget should sit, book a free 30-minute intro call and we will walk your category. Or request a free paid media audit and we will show you exactly where spend is being wasted across your current mix.