Run of site (ROS) is an advertising term in which a banner, image, or other online advertisement can appear on any page in any open placement within the targeted website. ROS allows publishers to place ads where they see fit, meaning the cost for advertisers is lower, but they must forfeit having control over where the ad is placed.
This advertising buying tactic rotates ads on various pages. Because of this, broader traffic is generated through reaching out to the general audience as opposed to a target audience. ROS rates are typically cheaper than specified ad placements and are paid through cost per thousand (CPM) impressions, or cost per click (CPC).
ROS works best when an ad campaign’s objective is to create brand awareness and reach a broad audience since there are very few options of targeting with placement. If the campaign is too niche, fewer leads or sales could result from using a ROS approach. It operates similarly to a run of network (RON) campaign, except the ads appear on one individual site instead of many sites. While the target audience for ROS still needs to be general, it can be more specific than running a campaign using RON because there is only one website instead of many.
Publishers find running ROS campaigns useful because it’s less time consuming, offers a straightforward setup of line items, and can be used as a method to monetize unfilled or unsold ad inventory. However, publishers don’t have much control as they can’t add frequency caps or creative rotation features, and they can’t set up ad unit targeting.