Hi George Vance   Thank you for getting back to me.  CoStar is LoopNet's parent company, so in that way we are the same. As for the real differences, CoStar is a data site and LoopNet is a marketing site.  CoStar has a large commercial database used to help real estate professionals research properties and understand market trends and conditions. CoStar is usually used by real estate brokers and owners with clients or looking for properties for themselves. We have over 175k subscribed to CoStar to have access to its data.  LoopNet has over 12 million visitors coming to its site monthly. LoopNet is geared towards buyers and tenants looking for their own space.  It is free to list on CoStar, but you must have a subscription to view the properties on CoStar. There is a cost to list properties on LoopNet, but millions of visitors can search properties on LoopNet at no charge.  - Karen Saccio LoopNet