Facebook and Zynga announced today that they have entered into a five-year strategic relationship that increases their shared commitment to social gaming on Facebook and expands use of Facebook Credits in Zynga’s games. The agreement provides a solid foundation for both companies to continue to work together, in spite of rumors that Zynga was gearing up to leave Facebook altogether.

“Facebook was a pioneer in opening their platform in 2007 and in just three years tens of millions of Facebook users play our games every day, from FarmVille and CafĂ© World to Treasure Isle and Mafia Wars,” said Zynga Founder and CEO Mark Pincus. “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.”

“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.”

Zynga is currently testing Facebook Credits in select games and will expand to more titles over the coming months. Terms of the agreement between Facebook and Zynga were not disclosed.