Bid4Spots is adapting its patent-pending "reverse auction" model to facilitate buying and selling advertising for independent online radio, writes MediaBuyerPlanner.

After just a year in operation, the Bid4Spots marketplace for terrestrial radio is used by 2,300 radio stations nationwide, 900 advertisers and more than 180 ad agencies - effectively making it the largest radio advertising network in the country, according to the company.

Applying the same principle - a reverse auction via which stations compete for advertisers' dollars and bid the ad rates down - Bid4Spots aims to harness what so far has been considered too fragmented to tame: independent, online-only radio broadcasting. The first auction will take place Jan. 16, 2007, and will continue each Tuesday thereafter. (A demo can be seen here.)

An Arbitron/Edison Media Research study reports that 52 million Americans listened to internet radio over a one-month period earlier this year; industry observers estimate that about 42 million of those listeners tune in to an estimated 25,000 independent online broadcasters.