The average price of a hotel room worldwide dropped 17 percent in the first six months of 2009 over last year, according to a Hotels.com Hotel Price Index. The drop in the average was driven by drops on all continents. In North America, prices were down 17 percent. Prices in Europe fell 16 percent. The index tracks prices paid by customers of 78,000 hotels at 13,000 locations around the world. Hotels.com has been tracking the index since January 2004.