Zynga accounted for one-tenth of Facebook's revenue in 2011

Better known for its ' CityVille' and ' FarmVille' games on Facebook, the US-based startup Zynga accounted for more than one-tenth of the social networking giant's total revenue in 2011, becoming its largest customer.

"Twelve per cent of our total revenue in 2011, and less than ten per cent in 2010 and 2009, came from a single customer, Zynga," Facebook said in the regulatory documents filed for its Initial Public Offer (IPO).

"This revenue consisted of payments processing fees related to Zynga's sales of virtual goods and from direct advertising purchased by Zynga," Facebook added.

About eight-year old social networking platform further said it generated USD 3.71 billion revenues last year, and USD 445.32 million of that came from Zynga.

Facebook also pointed out that there were risks involved in having such an inter-dependent relationship with Zynga.

The social networking firm said that if the use of Zynga games on its platform declined, if Zynga launched games on or migrated games to competing platforms, or if Facebook failed to maintain good relations with Zynga, the company may lose Zynga as a significant platform developer and the company's financial results may be adversely affected.

In May 2010, Facebook and Zynga entered into a five-year relationship to expand the use of Facebook Credits in Zynga's games.

As part of the agreement, Facebook retain a fee of up to 30 per cent of the face value of user purchases in Zynga's games on the Facebook Platform. This agreement will expire in May 2015.

Zynga, which started in 2007, has over 2,000 employees in many countries including India, while Facebook which was founded in 2004 employs around 3,000 employees globally.