Google has revealed the details behind its pay-per-action advertising.

The company yesterday announced that a new pricing model will allow advertisers to pay only when certain predetermined actions are completed on their site. Actions might include making a purchase or signing up for a newsletter. Advertisers will be able to create text or image ads as well as using Google's new text link ad format, which gives brief text descriptions that take on the characteristics of a publisher’s page.

Google said in a statement that the new model would mean advertisers have:

"the freedom of defining the value of a completed action, ultimately giving them more control over their advertising costs".

"Designed to complement Google's existing cost-per-click and cost-per-impression pricing models, pay-per-action pricing offers advertisers yet another choice, enabling them to reach their customers in a new way, and thereby better meeting their goals and objectives,"

The trial run will only be available to advertisers in the US initially.