An online advertising system integrates third party agents to permit the third party agents to participate in auctions to bid on a per opportunity basis. An advertising exchange module receives requests for opportunities to serve online advertisements to users. In response, an advertising exchange module applies one or more business rules to determine third party agents that qualify to serve the online advertisement. A bid gateway module generates and transmits requests for bids to the third party agents. The bid gateway module then receives bids from the third party agents in response to the requests for bids. The advertising exchange module then selects an advertisement based on the bid. The online advertisement exchange system provides a unified marketplace to permit integrator networks to bid on both ads pursuant to guaranteed contracts and ads not subject to guaranteed contracts (e.g., non-guaranteed ads). The online advertisement system further includes traffic management to allow the third parties to regulate bid requests sent from the online advertisement system. In some embodiments, the online advertising system caches bids, to efficiently implement the per opportunity auction, and transmits information, such as targeting information, to the third party agents to aid in the third party agents' formulation of bids.