Facebook says it's expanding its commitment to Facebook Credits -- a universal virtual currency system run by the social network allowing users to purchase digital goods in social games and applications (see image after the break) -- and revealed its payment terms for developers.

With Facebook Credits, which will be available alongside other virtual currency options from developers and payment providers, the social network will take a 30 percent cut of Credits spent, leaving developers to collect the remaining 70 percent of revenue. Facebook says it will use its cut to "[invest] heavily in the ecosystem."

The company recently expanded the Credits program to allow consumers to buy its virtual currency through PayPal. Other supported payment methods include various credit cards, 15 currencies, and mobile payments. Facebook believes this varied selection translates into "more people ready to spend, each with a higher likelihood of completing purchases".

Since moving into its beta phase (Credits began alpha testing in May 2009), the social network has tested the program with several big developers like Zynga, Playfish, RockYou, Crowdstar, Playdom, and 6waves, and will bring in more developers "over the next several months". Facebook says it plans to keep Credits in closed beta as it focuses on scaling the product to more users and studios.

"By providing a single, cross-application currency, our goal is to making transactions simpler for users, leading to a higher conversion rate for developers," says Deborah Liu, product marketer on the Facebook Developer Network team.

She continues, "... Our early testing has shown that users paying with Facebook Credits are significantly more likely to complete a purchase than the average Facebook user. These announcements and the continuation of our testing are part of our long-term commitment to you to build Facebook Credits into a product that is widely adopted by users and seamless to implement for developers."