• by David Goetzl  @dgoetzl, May 18, 2009

A company that has conducted online auctions for radio airtime since 2005 is stretching into local cable TV next month.

Bid4Spots will offer a weekly reverse auction, where advertisers post what they are willing to pay by CPM, and cable operators bid for their business.

The system is set up to cover the two minutes an hour that local cable operators can sell. Google TV Ads has an online system for that inventory, but has also tried to expand into brokering time on national TV networks.

The Bid4Spots auction will be conducted each Thursday for available airtime during the ensuing week. Advertisers will set parameters for their prospective buys, including by network, demographic targets and geographies. (They could look to run ads nationwide or in just target markets.)

Bid4Spots said its radio auction system saw business nearly double in 2008.