The Internet, which is poised to overtake outdoor as the fifth largest ad medium this year, is closing in on radio's fourth place ad market ranking, reports ZenithOptimedia in the latest quarterly revision of its ongoing global ad tracking study.

The revision, released this morning, estimates that Internet ad spending will break the double-digit market share in at least two countries - the U.K. (12.9 percent) and Sweden (10.5 percent) - marking the first time online ad spending has held such a significant ad market share in any major market in the world. Other markets projected to break the double-digit online ad share barrier by 2008 include: Australia, Israel, Japan, Norway, South Korea and Taiwan.

But despite ZenithOptimedia's projection of an 84 percent expansion in Internet ad spending between 2005 and 2008 (up from only a 76 percent rate of growth predicted in the agency's last forecast), the Publicis media agency doesn't expect it to break the double-digit barrier globally until 2011.

"The internet's share of global ad expenditure was 4.7 percent in 2005. We predict it will be 5.7 percent in 2006 and 7.3 percent in 2008," predicts the report. "At this rate the internet's ad share should reach double-digits worldwide by 2011."

The agency says much of the growth is coming from an acceleration in demand from smaller advertisers who are "embracing the affordability and targeting capabilities" of online advertising.

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