Podcast advertising revenue is growing, but not as fast as the podcast audience, according to the latest research from ZenithOptimedia.

By 2011, podcast ad spending is expected to grow to $43 million — but that amount comes to less than 0.2% of projected revenue for the total online advertising space.

Will podcast advertising ever catch up with podcast adoption?

Worldwide internet ad spending will jump to $44.6 billion in 2008, from about $36 billion, increasing its share of the market to 9.4% from 8.1%, according to ZenithOptimedia. “We predict internet advertising to pass three milestones over the next three years,” according to¬† ZenithOptimedia’s forecast, scheduled for release Dec. 3. “We expect it to overtake [...]