Google's plan to test radio advertising, known as Google Audio, is suffering from a lack of inventory, according to RBC Capital Markets analyst Jordan Rohan. This is the same Rohan, mind you, who predicted last month that Google would secure a big chunk of radio inventory within 30 days. So whatever happens, he's got it covered.

Google could solve its radio inventory problem by acquiring inventory from CBS Radio, and the scuttlebutt is that purchase is a possibility. Scuttlebutt before that, also incited by an RBC analyst, was that Google was interested in buying Clear Channel inventory, but that didn't happen.

Unless Google can strike a deal with a media company for radio inventory, Rohan says, the company's audio plans won't affect its bottom line in 2007 in the least. And there's still the question of whether automated ads are even appealing to the stations or radio listeners. Godspeed, Google, you're going to need it.