ROS

Detailed explanation

ROS, or Run of Site, is a delivery model where an advertiser's campaign is served across a publisher's general ad inventory rather than being pinned to one specific page, section, or placement. Instead of buying, say, only the homepage banner, a ROS buy lets the ad appear anywhere on the site where a matching slot is available, with the publisher's ad server distributing impressions across the full property.

The main advantage of ROS buying is reach and cost efficiency: because the inventory is not restricted to premium, high-demand placements, ROS impressions are typically priced lower than section-specific or homepage-guaranteed placements, making it a practical way to build volume and frequency across a site's whole audience. The trade-off is precision — a ROS campaign has less control over exactly where an ad appears, so it tends to suit awareness-oriented goals better than campaigns that depend on tight contextual alignment with specific content.

ROS is often positioned as the broad, budget-efficient counterpart to premium or section-targeted buys, and many media plans blend both: premium, contextually relevant placements for high-intent moments, and ROS inventory to extend reach and frequency across the rest of the site cost-effectively.