1. A system comprising: a storage unit configured to store local ad network tags and bids received with each respective ad network tag submitted by ad networks; a network interface; a processing unit in communication with said storage unit and said network interface, and configured to execute an ad engine, the ad engine configured to interact with a plurality of ad networks simultaneously and capable of receiving requests for ad network tags via the network interface from a user agent configured to render a page inclusive of an ad tag and at least one ad impression, and, in response to the requests for ad network tags, the ad engine further being capable of providing ad network tags to the user agent to cause the user agent to send ad requests based on the ad network tags, the ad engine, responsive to a request for an ad network tag from the user agent, further being configured to cause said processing unit to: simultaneously communicate a call to multiple ad network servers, in a first plurality of ad network partner servers, to request a bid from each of the multiple ad network partners for placing an ad with the user agent; receive bids from the first plurality of ad network partners servers; determine a highest bid from the ad network partners; determine a winning local ad network tag from the stored local ad network tags; determine whether a price associated with the winning local ad network tag is higher than the highest bid from the ad network partners; and in response to determining that the price associated with the winning local ad network tag is higher than the highest bid from the ad network partners, serve the winning local ad tag to the user agent; otherwise, serve an ad network tag associated with the highest bid from the ad network partners.