Described are methods, systems, and apparatus, including computer program products for domain selection for advertisement data in the delivery of website display ads. A request is received from a requester for indicia of one or more impression opportunities. A redirection URL and redirection type is received. One or more desired impression opportunities are determined. The indicia of the one or more impression opportunities are generated comprising indicia of the one or more desired impression opportunities. Redirection instructions are generated based on the redirection URL and redirection type. The indicia of the one or more impression opportunities and the redirection instructions are sent to the requester.