Google has completed the development of radio advertising system and begun a limited test allowing customers to buy ads via its online ad-buying system.

Google Audio Ads is working with more than 700 radio stations covering more than 200 metropolitan U.S. markets. Analysts expect Google Audio Ads to shake up the $20 billion annual U.S. radio advertising industry by offering a simplified Web-based purchasing process for radio ads to its existing base of hundreds of thousands of text advertisers

One executive at a big radio company said last month the industry was moving cautiously in its dealings with Google.Â

Bank concurred, saying: “There’s a real mixed emotion among radio operators.” On the one hand, Google’s entry may turn radio advertising into more of a commodity. “A disaster could occur if people who were buying spots offline started buying online at a lower pricing level,” Bank said.

Google is seeking to expand beyond the pay-per-click Web search advertising market it dominates to offer advertising across a range of traditional and new media formats ranging from newspapers to online video.