A supply-side platform (SSP) is an advertising technology platform that enables publishers to automate the selling, management, and optimization of their digital ad inventory across multiple ad exchanges and demand sources. SSP is also known as a sell-side platform. SSPs are a core component of programmatic advertising.
Traditionally, publishers manually sold ad space, which is still done today for premium ad space in some cases. Publishers needed a way to scale their selling processes and ensure that ad space was not left empty while maximizing the prices of ad impressions.
When supply-side platforms were first introduced, they were used for filling leftover inventory at lower prices. Today, the SSP is responsible for the programmatic selling of all ad inventory, working alongside display advertising ecosystems to maximize revenue.
Supply Side Platform vs. Demand Side Platform
Supply side platforms are equivalent to demand side platforms (DSP), except they are for advertisers, not marketers. Advertisers use SSPs to list their inventory, making it available programmatically to ad exchanges, ad networks, and demand side platforms. On the other hand, marketers use demand side platforms to buy advertising from multiple ad exchanges and ad networks programmatically.
Supply Side Platform vs. Ad Exchange
Supply side platforms are also not the same as ad exchanges. Ad exchanges do not manage ad inventory. Instead, an exchange is where publishers and marketers meet to buy and sell ads. It’s similar to an ecommerce marketplace (like Amazon) where multiple sellers can offer their products to multiple buyers.
However, some SSPs also provide an ad exchange as part of their platform.
How Does a Supply Side Platform Support the Ad Selling Process?
Supply side platforms are sometimes referred to as “yield-optimization platforms” because they are designed to ensure publishers fill their ad inventory with the best ads targeted at the right customers by dealing with multiple ad exchanges, ad networks, and DSPs.
Real-time Bidding
When an SSP has ad space available, it enables ad exchanges, ad networks, and DSPs to engage in real-time bidding (RTB) or a real-time auction for that ad space. For example, a visitor views a web page on the publisher’s site where ad space is available. The SSP starts a bidding process with selected advertisers. The winning bidder (typically the one with the highest price but not always) gets their ad placed in the open ad space.
Ad Network Optimization
Every ad network has its own set of requirements, including how much it’s willing to pay for ad space (CPM). With an SSP, a publisher can select which ad networks it wants to work with and how. These decisions are often made based on the ad space available or as general rules.
Price Floors
Publishers don’t have to accept any price for their ad impressions. They can set a minimum price for inventory, and when that minimum price is not met, they will fill the space with their own ads. Price floors can be set for specific buyers or channels.
Control Over Who Advertises
Publishers want to know that the brands that advertise on their properties meet certain standards. SSPs enable publishers to indicate which advertisers or advertisement categories (IAB categories) they will allow on their properties.
Reporting
Supply side platforms provide many reports to publishers to help them understand who is advertising with them. For example, reports such as how much ad inventory is bought for, who is bidding, and the number of ads an advertiser is buying are typically included.
Supply Side Platform Examples
Looking for a list of supply side platforms? Here are some of the most popular.
Google Ad Manager
Google Ad Manager is both a supply side platform and an ad exchange (AdX). It’s free for publishers that have over 5 million page views and offers full capabilities for managing ad inventory for video, native, and custom ad formats. It provides a unified first-price auction (the winning bidder pays the highest price bid) to help increase transparency and fairness. Publishers can leverage first-party data to enrich their inventory offerings.
Google Ad Manager works with open auctions, as well as direct-booked campaigns or Programmatic Guaranteed. It also ensures brand safety through certification by the Trustworthy Accountability Group against piracy, fraud, and malware, along with support for other industry initiatives.
OpenX
OpenX offers products for both publishers and advertisers. The supply side platform includes OpenX Bidder for real-time bidding, OpenX Mobile and OpenX Video for direct access to quality mobile and video advertisers, and OpenX Private Marketplaces for direct access to premium advertisers.
OpenX also offers AdExchange, an ad marketplace that gives publishers complete control over their ad platform, as well as OpenAudience, a solution to help them understand their audience better so they can match advertisers with highly targeted audiences.
Xandr (formerly AppNexus)
Xandr has a broad offering of solutions from an SSP to a DSP and ad exchange. It includes Xandr Invest, a DSP and connected TV offerings; Xandr Monetize, its SSP solution, and MonetizeTV, a connected TV solution for media companies.
Xandr is owned by AT&T giving it direct access to AT&T audience data and a strong focus on both digital advertising and connected TV advertising.
Magnite (formerly Rubicon Project)
The Rubicon Project changed its name to Magnite in mid-2020 after merging with another SSP with expertise in connected TV advertising, Telaria. The merging of supply side platforms has made Magnite one of the largest SSPs in the industry. In addition, it recently added to its capabilities advanced ad management for OTT and CTV with the acquisition of SpringServe.
Magnite provides both an SSP for publishers and a DSP for advertisers. It also offers a private marketplace (PMP) and Programmatic Guaranteed (PG) and Auction Package capabilities that give publishers complete control over their inventory and audiences.
Pubmatic
Pubmatic is an SSP for publishers and agencies. It includes private marketplaces, a premium header bidder solution, and support for real-time bidding. Another key feature of Pubmatic is its suite of ad quality tools that help publishers ensure the best ads are placed on their properties (it has strategic partnerships with ad quality enterprises, The Media Trust, and Confiant).
Pubmatic also includes solutions for buyers, including its Media Buying Console (real-time data and proactive deal health intelligence), Inventory Quality (vetting publishers, filtering invalid traffic, and ensuring brand safety), and access to private marketplaces.
FAQ
What is the difference between an SSP and a DSP?
A supply-side platform (SSP) is used by publishers to sell and manage their ad inventory, while a demand-side platform (DSP) is used by advertisers and marketers to buy ad placements programmatically. SSPs aim to maximize revenue for publishers by connecting them to multiple demand sources, whereas DSPs aim to help buyers reach their target audiences at the best price. Both interact through ad exchanges where real-time bidding takes place.
How do supply-side platforms use real-time bidding?
When a user visits a publisher’s website, the SSP sends available ad inventory information to ad exchanges and DSPs, triggering an auction that completes in milliseconds. Advertisers bid on the impression based on the user’s profile and the value of the placement, and the winning ad is displayed to the visitor. This real-time bidding process ensures publishers get competitive pricing while advertisers reach relevant audiences.
Why are supply-side platforms important for publishers?
SSPs automate and optimize the ad selling process, ensuring publishers fill their inventory at the highest possible prices without managing each sale manually. They provide controls such as price floors, advertiser category filters, and brand safety settings that give publishers governance over what appears on their properties. SSPs also offer reporting and analytics that help publishers understand demand patterns and optimize their monetization strategy. As the industry adapts to evolving data privacy regulations, SSPs are increasingly investing in privacy-compliant targeting solutions.
Related Terms
- Return on Ad Spend (ROAS) — Key metric for measuring advertising efficiency across SSP-managed inventory
- Native Advertising — Ad format increasingly sold through SSPs alongside standard display inventory
- Data Clean Room — Privacy-safe environment where publishers and advertisers can match audience data
- Cookieless Tracking — Emerging approaches to audience targeting as third-party cookies are deprecated