$43.6B U.S. agency revenue
The year was particularly fruitful for Google, which commands a 65.9% share of all U.S. searches. Google's share of paid search expenditures in Q4 was even more impressive at 81.8% of all U.S. PPC spend.
In addition, cost-per-clicks declined 8.6% in the fourth quarter versus the year-earlier period, even as impressions and clickthrough rates increased. The company's study was based on more than 79 billion impressions and 1.7 billion clicks on Google and Yahoo/Bing search networks, Google AdEx and other display networks.