Facebook's revenue doubled to $1.6 billion in 2011's first half, a source with knowledge of its financials told Reuters, underscoring its appeal to advertisers while it grapples with intensifying competition from the likes of Google Inc.

Net income in the first half of 2011 came to almost $500 million, according to the source, who wished to remain anonymous because privately held Facebook does not disclose its results.

Facebook's stronger results come as investors have pushed its valuation to roughly $80 billion in private markets, with many industry observers expecting the world's No. 1 Internet social network to go public in 2012.

Its growing popularity among adver-

tisers and its 750 million users has pressured entrenched Web companies such as Yahoo Inc, which ousted its chief executive Carol Bartz on Tuesday. "We really see Facebook as becoming like the operating system for delivering ads on the Internet," said Dave Williams, the CEO of Blinq Media, which runs ad campaigns for companies on Facebook.

Search leader Google Inc launched Google+, a rival social network in June that attracted more than 10 million users in its first two weeks. Google has yet to offer ads on its social network, but it is trying to increase Google+'s appeal to consumers by offering games such as Zynga Poker and Rovio's Angry Birds.

Some venture capitalists and industry experts see early signs that Google* is headed down the right path in taking a bite out of Facebook.