A content provider may provide public access to a content item set, but may be unable to achieve sufficient revenue to sustain the administrative costs and ongoing development of the content item set. Instead, the content provider may develop relationships with one or more referrers (e.g., search engines.) When a user requests a content item, the content provider may determine whether the request results from a referral by a sponsoring referrer, and based on this determination may provide either a full version or a limited version of the content item. The referrer benefits by providing its users with free access to the content item set, which may be unavailable from non-sponsoring competitors, and in exchange may share advertising revenue with the content provider. This arrangement achieves sustaining sponsorship of the content provider while extending full and free access to the content item set to users of sponsoring referrers.