In addition to audited ad impressions, the companies also called for publishers to certify that their underlying ad-counting process is consistent and reliable by 2008. They warned that only audited and certified numbers would be used for payment against their interactive marketing campaigns.

"Now that we have a protocol in place and measurement guidelines, it's just a matter of encouraging our online partners to act now," said Brad Santeler, a spokesman for Kimberly-Clark, one of the big brand marketers urging Internet publishers and ad-serving companies to adopt a uniform ad reporting system. The other large marketers to say they will require audits by next year include BMW, HP, ING and Pepsi.

The Interactive Advertising Bureau in 2004 issued ad measurement guidelines setting specific rules for when and how an ad impression is counted, as well as procedures for the auditing and certification process. Last spring, the IAB also announced guidelines for broadband video commercials, stating that a video ad should not be counted as displayed until its buffered stream has begun.

The overall aim of the guidelines is to ensure consistency in the online marketplace, where companies are spending an increasing proportion of their ad budgets. Leading industry forecaster Robert Coen, senior vice president and director of forecasting for Universal McCann, predicts that Internet spending, excluding search, will surge to $9.7 billion this year, a 25 percent increase from 2005.

Among large Web sites and ad serving networks that have already completed certification are AOL, CNET the Walt Disney Internet Group and DoubleClick. Others that have committed to completing the process during 2006 include iVillage, 24/7 Real Media, Forbes.com and The New York Times.

"Many of the companies today already are in the process or are planning to have audited results anyway," said Mary Bermel, director of interactive and new media for HP. "This makes it much more formal, and we stand beside the notion that we will only advertise with sites that are audited." She added that the marketers' push was a next step to make sure that sites follow the same standard.

Sean Harvey, senior production manager for the Dart platform at DoubleClick, said he welcomed the marketers' statement. "The ultimate objective is that everyone be certified on the buy-side and the sell-side," he said. "I think the majority of major players will all be certified by 2007."

Kimberly-Clark's Santeler noted that smaller online publishers need to be on board too. "We can get pretty vertical with our branding, so major publishers may not be the sites we choose to use," he said.

The IAB guidelines recommend that online publishers hire independent, third-party auditors to conduct the certification process but doesn't designate specific firms. Major accounting firms such as PricewaterhouseCoopers and Ernst & Young are among those that typically handle ad audits with oversight from the nonprofit Media Rating Council.

"The marketplace ultimately chooses who are the accepted auditors and certifiers," said Greg Stuart, IAB's chief executive. He said he expected other large marketers to come forward to call for audited ad numbers from Web publishers.

Shankar Gupta contributed to this article.

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