The 2008 figure represents 13% of the American population over the age of 12, and 17.5% of the total online population (188 million in 2007, according to separate figures from eMarketer.

In addition to metrics documenting growth in the overall audience, the latest round of research from Arbitron and Edison focused on the substantial overlap between online radio listeners and social network users.

Among the findings released by the research partners, 63% of online listeners maintain a profile on sites like MySpace, Facebook, or Linked-In, compared with 24% of all Americans 12 or older. Twenty-eight percent of online listeners have a MySpace profile and 24% a profile on Linked-In. What's more, they're heavy users of these sites, one-third of the overlapping cohort visit the sites nearly every day, if not several times a day.

The Arbitron/Edison report comes amid a flurry of online radio deals.

Last week, CBS and AOL struck a deal that will make a broad array of content available to AOL users, including over 150 music, news, talk and sports stations. In addition to providing content, CBS is assuming responsibility for ad sales for all of AOL's online stations, which number over 200, as well as the 150 stations it brings to the table

Shortly afterwards, Cox Radio said it will provide program information from all its stations around the U.S. to RadioTime, which allows Internet users to browse, search and listen to online radio from terrestrial stations with its RadioGuide interface. The station IDs and other information will appear on Radio Guide alongside the streaming audio. Cox joins about 100 other radio networks and a total of about 100,000 programs on the RadioTime site.

In January, TargetSpot (an online radio ad service developed by CBS Radio and venture capitalists) signed up six new partners, including inTune.fm, a popular audio application on Facebook.

Last year also saw numerous deals. In November, Triton Media Group bought Excelsior Radio Networks and its two subsidiaries, Dial Global and MJI Interactive. In July, Katz Media Group acquired Net Radio Sales (renamed Katz Net Radio Sales). Also in July, Ronning Lipset Radio announced that it had partnered with Corstarr to use its Adcor technology for delivering Internet radio ads.

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