In its largest acquisition yet, internet search giant Google will purchase online advertising firm DoubleClick for 3.1 billion dollars, US media reported Saturday. The acquisition had pitted Google against Microsoft Corp, which also wanted to acquire DoubleClick, a key player in the 28.8 billion dollar inte2/Q advertising business, the San Francisco Chronicle reported. Yahoo and AOL had also shown interest in the acquisition, according to dpa. The deal, which was announced Friday after the close of markets, is nearly twice the amount Google paid last year, when it acquired video site YouTube for 1.65 billion dollars. DoubleClick is controlled by private equity firms Hellman & Friedman and JMI Equity, which acquired the firm in 2005 for 1.1 billion dollars. New York-based DoubleClick specializes in online display ads that direct customers to clients' websites when they click on an online ad. It operates 17 offices and 15 data centres worldwide and employs 1,200 people. -- SPA