Facebook games aren't tracked in terms of sales, so it's difficult to find accurate revenue estimates. Nevertheless, since more game companies are going social, IGN decided to put together a graphic to see how much revenue social titles are bringing in.

While social game companies don't share their numbers, an NPD study last year found that 10 percent of the people who play Facebook games pay real money to buy in-game items or currency and a SocialGold study found that the average player who actually pays real money spends about $55. Putting the two together, it's possible to estimate how Facebook games stack up to the top 10 games of 2010 in terms of paying players and revenue generated. Players were rounded to the nearest half million and revenues were rounded to the nearest $50 million:

It looks like Call of Duty: Black Ops was the only game that had more players and made more money than any Facebook game. It's no wonder that Zynga is valued higher than Electronic Arts. This may not be the most accurate estimate, but it's interesting to see ballpark figures nonetheless.