($4.19bn), research firm eMarketer says. The social network is expected to earn $US3.8bn worldwide this year in advertising revenue, eMarketer said, up 104 per cent from the $US1.86bn it raked in last year. The research firm also said revenue from Facebook Credits, the currency used on the site, is estimated to reach $US470m, up from $US140m 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 $US5.78bn in worldwide ad revenue in 2012, eMarketer estimated.