The firm says that by letting developers offer Credits on Web sites, they can "offer a more unified app experience to users beyond apps on Facebook".

On its developer blog, it reveals that gaming portal GameHouse is trialling the system for Collapse! Blast. Players will pay for the game using Facebook Credits instead of the normal options of cards and PayPal.

The experiment is still in its infancy with Facebook gathering developer feedback and inviting more players to sign up as it looks at ways of tightening its grip on the virtual currency market.

In July it began forcing developers to use its virtual currency for payment processing within Facebook, although the plans had to be tweaked after an anti-trust complaint from US public interest group Consumer Watchdog.

The watchdog claims that Facebook controls well over 50% of the estimated $2.1 billion market for virtual goods offered in social gaming.