Facebook's growth is so strong that revenue this year may tap $4.3 billion, twice its previously estimated worth, market researcher eMarketer reports.

Previous unconfirmed reports have tagged Facebook's revenue between $1.5 billion and $2 billion, Reuters and others have reported. The Menlo Park, Calif.-based social network site has not commented on any reports.

Facebook's revenue stream is split: about $3.8 billion is believed to come from advertising with the remainder for Facebook Credits, the e-currency required for gaming and some other activities, New York-based eMarketer said.

Meanwhile, the researchers said it believed Facebook's 2010 revenue was $2 billion, a 150 percent jump from 2009. Advertising revenue last year was about $1.9 billion, so growth in Facebook Credits shows the site has been successful in creating its own currency.

EMarketer also says Facebook is the U.S. leader in online ad and display ad revenue, beating Yahoo and Google.

Facebook has a 16.3 percent share, followed by Yahoo's 13.1 percent and Google's 9.3 percent, based upon full-year projections.

Since Yahoo fired CEO Carol Bartz this month and the board of the Sunnyvale, Calif.-based company has hired investment bankers, Facebook might seek to acquire Yahoo as a means of going public. That would be a so-called reverse takeover.

Facebook is privately held and is widely believed to have more than 500 shareholders, in addition to major venture capital investors Accel Partners and Goldman Sachs. Under U.S. law, it will be required to disclose financial results to the Securities and Exchange Commission, most likely early in 2012.

Facebook CEO Mark Zuckerberg is 27. A year ago this week, he donated $100 million to the Newark, N.J., public schools in the first effort to set up a private foundation.