Google today announced a limited beta test of pay-per-action advertising, a new pricing model for certain AdSense ads on its content network that pits the company squarely against affiliate programs.

Under the new pricing model, advertisers will decide what kind of action they are willing to pay for, such as a sale, newsletter sign-up, or other conversion. The advertiser can set a value for that action that publishers will be paid. Google will monitor the conversions through tracking codes on the advertiser's site.

Although a pay-per-action model shifts more risk to publishers, since they don't get paid unless a visitor clicks and completes the pre-defined conversion, the payoff will usually be higher than CPC commissions, said Rob Kniaz, product manager for Google's ad products.

"It does shift the burden of conversion to the publisher, but it's a higher value ad unit," he said. In addition, publishers have more flexibility in encouraging users to take advantage of the offer being presented, by recommending or describing the advertiser's service, he said.

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