DoubleClick, the online ad firm, which is in talks with Microsoft and Google for a possible sale, is in the process of launching an online ad auction exchange, reports NYT. In this online exchange, to be launched in Q3, publishers and ad buyers will participate in auctions for ad space. It has signed up 35 Web publishers, advertising networks, agencies and advertisers to test the system. Two of the testers are Advertising.com, a large ad network, and Media Contacts, an interactive media buyer that is part of Havas. DoubleClick will charge a commission for each ad impression traded on its exchange.