Condos seem to be driving the increase in the inventory of unsold homes on the market. That's what emerged from an analysis of Tampa Bay area home sales data for October.

About 41,000 homes were listed for sale last month in Pinellas, Pasco and Hillsborough counties. The biggest growth occurred among condos in Hillsborough.

The number of condos for sale in and around Tampa grew from 1,976 to 4,032 from October 2006 to October 2007. The condos bloated the county's overall inventory from 13,229 to 15,092 year over year.

Several forces seem to be at play. First, apartment buildings converted to condos have swollen the market. Second, investors are trying to sell units in recently completed condo towers in downtown Tampa and Channelside.

I would suggest a third possible cause: As single-family home prices come down off their housing boom highs, buyers no longer need to economize by buying into less expensive condos.