While the $100 billion global classified advertising market is still largely the purview of newspapers (on the mainstream media side), thanks to their online outlets, TV, cable and radio stations are making inroads into print publications’ once secure monopoly. A study by Classified Intelligence, found that TV station websites in all top 50 U.S. markets offer classifieds, as do radio sites in 47 of the top 50 markets and four out of five of the top MSO cable systems. Internationally, the study found online classified growth to be fairly slow, though Germany, the U.K., Australia and Canada. The report’s other mainline findings included:

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—For TV station classified sites, real estate is the strongest category in the top 10 markets. Below the top 10, real estate, automotive and jobs are relatively even.

—Cable sites have naturally sought to emphasize their video capabilities with VOD listings that rely on the information contained in set-top boxes to target specific consumers. Comcast, for example, has a “classifieds on demand” service that lets marketers convert text, print, catalog pages and internet banner ads into auto listings. Of the top five MSOs – Comcast, Time Warner, Charter, Cox and Cablevision, only Charter has no classified offerings.

—In the case of radio stations, the top 50 markets have tended to ignore the use of online classified ads. Penetration is more perceptible when it comes to markets 11- to 50, especially for autos and jobs.

While the revenue from TV, cable and radio sites is likely to remain small for the near term, these sites do have certain advantages. As the extension of deals like Yahoo’s newspaper consortium show this week, online sites are trying to attach the established local brand to create new revenue streams, while smaller dailies try to tap the broader the web offers. The report can be downloaded for free here.