Amazon stated that it sells more e-books for its electronic reading device Kindle than paperback and hardback print editions combined. 

The news that the online retailer has sold more than three times as many Kindle books so far this year as in the same period of 2010 came as the Association of American Publishers reported that US e-book revenues had grown 146 per cent in March over the same month a year earlier. Amazon only released unit sales data rather than comparable revenue figures, and Kindle editions typically sell for lower prices than print titles.   Source:  Financial Times