Google didn’t keep the wraps on their affiliate like Pay Per Action ads for long. Introduced in March, these ads have already come out of beta.

Google announced today the worldwide expansion of its pay-per-action advertising beta. Pay-per-action is a new pricing model that allows advertisers to pay only when a pre-defined action is completed on their site, such as when a user makes a purchase, signs up for a newsletter, or completes any other clearly defined action. Since the initial launch of the pay-per-action advertising beta in March 2007, many advertisers who have used the new pricing model are pleased with the opportunity to have more ways to promote their products and services online.

Source: Google Press Release

Additional Resources:

• For Advertisers: Guide to creating pay per action ads
• For Publishers: Guide to creating pay per action ads (Search Engine Land Article)