eMarketer has released a study that found the audience for podcasts in the United States will increase to 25 million by 2008 and 50 million by 2010.

The study also forecasts that the active podcast audience in the United States can be expected to reach three million this year, 7.5 million in 2008 and 15 million in 2010.

eMarketer Editorial Director Mike Chapman says that podcasting faces tough competition from the U.S. radio which reaches 200 million listeners. He warns that, "Podcasting is not set to become a new mass-market venue, at least for the next half decade."

Despite this, online advertisers are paying close attention to this new phenomenon and according to eMarketer's analysis, advertising spending on podcasting will reach $80 million this year and $300 million by 2010.