• by Mark Walsh  @markfwal, January 18, 2011

Ad spending on Facebook will reach $4.05 billion worldwide in 2011--more than double last year's $1.86 billion total in global ad revenues, according to a new estimate from eMarketer. By 2012, worldwide ad spending on Facebook is expected to reach $5.74 billion, up 42% over 2011.

With its nearly $2 billion in revenue this year, Facebook is already reported to be worth a whopping $50 billion based on a recent $500 million investment by Goldman Sachs. The company is widely expected to go public next year.

"2010 was the year that Facebook firmly established itself as a major force, not only in social network advertising, but all of online advertising," said eMarketer principal analyst Debra Aho Williamson, in an article released today. "In 2011, its global presence is something multinational advertisers can't ignore."

The projected $4 billion in ad spending on Facebook in 2011 is expected to be roughly evenly split between the U.S. and international markets.

Spending on social media advertising overall in the U.S. will increase 55% to $3 billion this year, with social media accounting for 10.8% of all online ad dollars. Worldwide, where social network ad spending will rise 71.6% to nearly $6 billion, that proportion will be somewhat lower, at 8.7%.

Not every social site is benefiting from the growth in spending in the category. Ad revenue at MySpace, which last week slashed about half its staff, is predicted to fall to $184 million in 2011 from $288 million last year and $470 million in 2009. Facebook's rise has come directly at the expense of the former No. 1 social networking property.

With an official user base of 500 million, now estimated closer to 600 million, Facebook could end up beating even the bullish projections from eMarketer for this year. "If Facebook can continue to increase its global user base and boost the amount of revenue it generates per user, it could even surpass these forecasts," said Williamson. The bulk of the company's revenue to date is coming from small and medium-sized businesses using its self-serve ad system.