This article originally appears on MediaPost.

Header bidding has taken up quite a bit of bandwidth among ad-tech executives and industry stakeholders. While it’s traditionally been known as a supply-side tool to help publishers create more competition, header bidding has quickly become a “must-have” for marketers to access valuable ad inventory.

To rewind, header bidding offers visibility into both direct-sold inventory and inventory offered via exchanges at the same time. It enables advertisers to see a large percentage of users instead of only those that weren’t already bought through guaranteed buys. They are then able to compete for a greater share of a publisher’s inventory.

OpenX and MediaMath partnered recently to put header bidding to the test for the buy side. The ad-tech firms did so by offering OpenX Bidder-enabled publishers to MediaMath‘s TerminalOne Platform for advertisers and marketers. The move gives MediaMath users the ability to compete for a greater share of a publisher’s inventory.

Tanuj Joshi, VP, global media partnerships at MediaMath, broke down the key findings for RTBlog: “We looked at audience data through our TerminalOne platform and OpenX’s header bidding solution, OpenX Bidder, to see if advertisers could get stronger incremental user reach through header bidding. Of the matched users, we found that OpenX Bidder adds 24% more users and 16% more so-called ‘high-value’ users to what tag-based publishers already provided. Of all users in the ad request sample, one more new user was added for every 24 opportunities to engage with a customer.”

Joshi said MediaMath recommends that advertisers buy from header bidding-enabled publishers, as well as tag-based publishers in order to get maximum reach and avoid missing users. He also said that advertisers can more effectively access high-value users through header bidding than on publishers that are only integrated through exchange tags. They can get additional reach when new users are added to the pool of known users.

“It’s well known that header bidding has significant benefits for the sell side, so it was important for us to demonstrate quantifiably that there are significant benefits for the buy side as well,” Natrian Maxwell, director, demand services, OpenX, told RTBlog via email. “This is the first time we have data that proves header bidding increases reach for advertisers.”

More results from the OpenX and MediaMath‘s test can be accessed here.