OSD revenue increased primarily as a result of growth in online advertising revenue. Online advertising revenue grew $100 million or 21% to $572 million, reflecting continued growth in search and display advertising revenue, offset in part by decreased third party advertising revenue. Search revenue grew due to our Yahoo! alliance, increased volumes reflecting general market growth, and relative share gains in the U.S., offset in part by decreased revenue per search primarily related to challenges associated with optimizing the adCenter platform for the new mix and volume of traffic from the combined Yahoo! and Bing properties. As of September 30, 2011, according to third-party sources, Bing organic U.S. market share grew over 31% from September 30, 2010 to approximately 15%. Bing-powered U.S. market share, including Yahoo! properties, grew over 13% during this same time period to approximately 27%.
OSD operating loss decreased due to higher revenue and lower sales and marketing expenses, offset in part by increased cost of revenue. Sales and marketing expenses decreased $59 million or 25% due mainly to decreased marketing spend. Cost of revenue grew $85 million driven by increased traffic acquisition costs.