• Business Week, Wednesday, February 14, 2007 10:47 AM

Podcasting never quite took off as an ad platform. It's just been forgotten in the wake of Web 2.0 phenomena like online video and social networking. But if Clear Channel, CBS Radio and Rush Limbaugh have entered the podcast market, there must be something to it.

According to research aggregator eMarketer, podcasting continues to grow in penetration and influence, meaning the talk-radio alternative is now poised to grab a bigger slice of the online ad pie.

Last year, spending on podcasts was just $80 million, but eMarketer expects that number to hit $400 million by 2011, according to a report scheduled for release later this week.

Part of the reason is Google's expected entry into the market. Given its early struggles with terrestrial radio, it's only natural that the Internet giant should shift attention to its online cousin. Within five years, report author James Belcher believes Google will develop the capability to insert audio ads into podcasts based on keywords.

Growth will also be spurred by the continued development of third-party services like ratings and demographic measurement. Podtrac is one such firm; the company has already unveiled a free online service that lets advertisers search for audience information for podcasts based on demographics, size and other characteristics. Podtrac helps the top 5,000 or so podcasters connect with advertisers.

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