Facebook revenue estimated at $4.27 billion

Facebook's global revenue is expected to double this year to $4.27 billion, research firm eMarketer said Tuesday.

The Palo Alto, California-based social network is expected to earn $3.8 billion worldwide this year in advertising revenue, eMarketer said, up 104 percent from the $1.86 billion it raked in last year.

The research firm also said revenue from Facebook Credits, the currency used on the site, is estimated to reach $470 million, up from $140 million last year.

"Facebook's revenue streams will continue to diversify, with ads representing a decreasing proportion of total revenue while other sources such as Facebook Credits will grow," eMarketer principal analyst Debra Aho Williamson said in a statement.

Facebook will earn $5.78 billion in worldwide ad revenue in 2012, eMarketer estimated.

As a privately held company Facebook does not disclose figures on its financial performance.

Facebook, the world's largest social network with more than 750 million members, is expected to go public next year and would have to open its books to conduct an initial public offering.