Google has expanded the pay per action (PPA) ad system it started testing in March internationally.

The move, which allows advertisers to only pay fees to Google if users complete a defined task (such as signing up for a newsletter), follows a closed beta trial in the US.

In a statement, the web giant said the system could now be used by any advertiser worldwide, as long as they had generated more than 500 conversions from other Google campaigns in the last 30 days:

“Starting today, advertisers in the beta will see an alert in their AdWords account informing them that they can now create pay-per-action campaigns.

“Going forward, advertisers who have enabled AdWords conversion tracking and received more than 500 conversions from their CPC and CPM-based campaigns in the past 30 days will be automatically added to the beta on a rolling basis.”

The PPA system clearly signals a move by Google into affiliate marketing – although it remains to be seen how it will affect existing affiliate networks.

Through it, the PPA ads are displayed separately from Google’s CPM and CPC ads, and can take the form of text, images or in-line text links.