The Interactive Advertising Bureau on Monday unveiled standards for helping buyers determine whether the seller of online advertising has met the promised level of ad viewership, in an attempt to eliminate a major obstacle to some companies advertising on the web.

Also on Monday, the IAB reported that online advertising revenue reached a record $2.43 billion in the third quarter, a 35.3 percent boost from the same period a year ago and the eighth consecutive quarterly increase.

On the guidelines, the move is intended to sustain the growth of Internet advertising spending by simplifying the buying and selling process for advertisers, marketers and publishers, the IAB said. By offering a detailed definition for counting an "ad impression," the group said it is providing a critical component in establishing consistent and accurate online advertising measurements across publishers and ad-serving technologies.

An ad impression is a measure of a response from an ad delivery system to an ad request from a user's browser.

"This is the first time any medium has come up with a global standard for advertising measurement," Greg Stuart, president and chief executive for IAB, said.

The guidelines are supported by about 35 out of the 37 major online advertising server technologies worldwide, the IAB said. This is important because many technologies today count ad impressions differently, making it difficult for ad agencies and publishers to agree on a measurement system.

"This was a real problem," Stuart said. "Some marketers would not spend money on online advertising because they weren't comfortable with the numbers."

Among the recommendations in the guidelines, which are voluntary, is counting an impression once the browser receives the advertising, as opposed to some systems that count an impression when the browser makes the request.

In addition, the IAB is offering proposals for handling third-party independent auditing and certification guidelines for all ad-serving applications used in the buying and selling process. The certification recommendation is for ad impressions only.

According to the IAB's Ad Revenue Report, conducted independently by PricewaterhouseCoopers, advertisers spent 2.4 percent more in the third quarter than in the previous quarter. Sales in the first nine months of the year totaled slightly more than $7 billion, which is nearly as much as the $7.3 billion reported for all of 2003.

Online advertising makes up a small portion of the $250 billion expected to be spent on advertising this year, but its growth is forecast to continue, exceeding ad revenues for the magazine industry in a year or two, Stuart said.

"We won't see a major slowdown (in online advertising), but we won't see the same level of double-digit growth (in the years ahead)," Stuart said.