Not surprisingly, Amazon is the most lucrative sales channel for eBooks, according to Revealing the Business of eBooks: 2009-2012, the fourth eBook survey of publishers conducted by Aptara and Publisher’s Weekly. The study, which was conducted in April, found that 68 percent of eBook publishers sell via Amazon making it the most popular sales channel for eBooks, followed by Apple’s iBookstore which is used by 58 percent of eBook publishers.

The study found that 4 out of 5 publishers are now publishing eBooks, which is an increase of 30 percent from three years ago. Making titles available as eBooks is helping drive sales. According to the report, 36 percent of eBook publishers are “realizing double-digit annual eBook revenues,” which is up 100 percent since last year. Still, the report points out that 65 percent of eBook publishers have converted less than half of their backlist titles into eBooks.

Curiously, the report found that while 31 percent of eBook publishers produce enhanced eBooks, only 12 percent of those publishers are finding that these enhancements have a positive impact on sales.