Facebook said today it has entered into a five-year relationship with Zynga, the social networking gaming company behind the popular FarmVille and Mafia Wars.

Under the deal, Zynga will expand its use of Facebook Credits in its games. The deal signals Zynga's commitment to social gaming on Facebook. Terms of the relationship were not disclosed.

"Facebook was a pioneer in opening their platform in 2007 and in just three years tens of millions of Facebook users play our games everyday, from FarmVille and Cafe World to Treasure Isle and Mafia Wars," said Mark Pincus, founder and chief executive officer at Zynga.

"We are excited about Facebook's long-term commitment to social gaming and Zynga, and look forward to working with them and other platform providers to bring the best social gaming experience to users worldwide."

Facebook is in the process of introducing its Credits as the primary method of payment on its platform, and will take 30 percent of all transactions.

Zynga is currently testing Facebook Credits in a handful of its games and will expand to more titles in the coming months.

"We are pleased to enter into a new agreement with Zynga to enhance the experience for Facebook users who play Zynga games," said Sheryl Sandberg, chief operating officer at Facebook.

"We look forward to continuing our work with Zynga and all of our developers to increase the opportunities on our platform."