The US audience for podcasts will more than double in the next two years, growing from 6.5 million (active weekly downloaders) in 2007 to 14 million in 2009.

According to a new report by eMarketer

• The total US podcast audience reached 18.5 million in 2007;
• The total audience will increase by 251% to 65 million in 2012;
• There are currently 6.5 million people that download one or more podcasts per week; and
• In five years, there will be 25 million active podcast downloaders.

As The Podcast Audience Grows, Advertisers Will Follow

”As the US podcasting industry matures it is unquestionably creating a listening audience,” says Paul Verna, eMarketer Senior Analyst. “Along with a larger audience comes increases in advertising spending tied to podcasts.”

US spending on podcast-related advertising (including sponsorships) will rise to $435 million in 2012, up from $165 million in 2007:

Verna identifies a number of factors driving the growth of the podcast-user base:

• Greater ease of consumption for podcast content
• Growing awareness of podcasting
• Terrestrial radio‚Äôs use and promotion of podcasting
• Increased penetration of portable players
• The evolution of smart phones and proliferation of affordable mobile data plans

While eMarketer’s podcasting statistics paint a rosy picture for podcasts, they actually appear to be based on a fairly limited idea of podcasting (radio-style audio podcasts). We’re checking into this with eMarketer to see if we can get clarification on this.