Google has been working on a pay-per-action (PPA) model by which, instead of paying per impression or per click on served ads, advertisers only make payment when users complete a predefined action. Such activities can include making a purchase or registering for a newsletter, reports MediaPost.

Today Google expands its PPA beta to a number of advertisers on AdWords.

Beginning today, advertisers with conversion tracking and over 500 conversions from CPC- or CPM-based campaigns in the past month will be added to the PPA beta on a rolling basis. Options to build campaigns and set the parameters for conversions will appear in their AdWords accounts.

Some marketers perceive PPA as a new attempt by Google to reignite business from advertisers who may feel burned by ever-escalating PPC costs and a paltry ROI.

The global beta, released in March, launched in 24 languages.