The Facebook virtual economy is rapidly growing and evolving to include more complex, graphic-rich games, according to companies who facilitate payments for Facebook applications.

It's already happening in full force in China. A in revenue last year, primarily through selling virtual goods.

Spare Change CEO Mark Rose, whose company handles direct payments for Facebook applications, discussed the virtual goods industry within Facebook with The Standard. According to Rose, Facebook games generating the most revenue include role-playing games such as Mob Wars, casino and card games such as poker, and games that build up a virtual world, such as YoVille.

But this is changing, said Jason Bailey, the CEO of Super Rewards, a company that helps developers integrate offers from advertisers and direct payments into their games.

"As the platform evolves we are seeing more and more immersive environments, mini-worlds of the calibre we commonly see...in console games," he told The Standard.