Facebook has been busy meeting with large developers on its platform, trying to get them to sign deals to exclusively use its virtual currency, Credits, in their applications. So far, it has CrowdStar and LOLapps using Credits exclusively as the direct payment method, with rivals like Zynga participating but also using alternatives.

Now, there’s another big developer joining the exclusive list: RockYou. The company said say in a post about using virtual currency in its big social game, Zoo World. Here’s the key part: “RockYou is NOT doing away with Wildlife Point items to be replaced by Facebook Credits ($0.10 each). But all CASH purchases will require facebook credits within a year (Facebook requirement).”

> Read the full story on Inside Social Games.