According to the newest figures from Bowker Market Research, online retailers accounted for 39% of all book sales in 2011, up from 30% in 2010. The increase gave the online channel, led by Amazon and, a commanding lead over bookstore chains as the largest outlet for sales. The chains, weakened by the loss of Borders in the year, accounted for only 26% of sales, down from 29% in 2010. Data from Bowker, and other sources, suggest that the gains posted by the e-tailers are being driven mostly by e-book sales. Furthermore, the online channel, much like its bricks-and-mortar competitors, is seeing, if not a decline in print book sales, at least slowing growth.

Barnes & Noble said as much when it commented on results for the 2011 holiday. In its third quarter, sales through rose 31.7%, driven by sales of Nook devices and e-content, as sales of physical products sold through the site fell, CEO William Lynch said in a conference call. At the much smaller Books-A-Million, figures in its 10-k filing with the Securities and Exchange Commission showed that print book sales through its online arm fell 18% as e-book sales rose 133% in 2011.

It was a different story at Amazon, however. In last year’s fourth quarter, print book sales rose by double digits, something the company acknowledged was a bit of a surprise. “Physical books’ unit growth was double digit in Q4 year-over-year, which we were very pleased with, if you think about the shift to digital content and just the really rapid growth on the Kindle side,” CFO Tom Szkutak said. In the first quarter of 2012, Amazon said, sales of both digital and print books rose again.

Amazon’s stronger performance with print sales compared to is borne out in Bowker figures for 2010 and 2011, which show just how much the product mix is shifting at the two major print/digital retailers. In 2011,’s reliance on e-book sales rose significantly, with the format accounting for 29% of sales compared to 10% in 2010. Amazon, which appears to have captured more former Borders customers than, saw e-books’ share of sales rise to 13% in 2011 from 5% in the previous year. At e-book sales appear to be taking away from hardcover sales, whose percentage of sales fell from 43% to 35%. Trade paperbacks’ share of sales fell by five percentage points in the year. The decline in hardcover’s percentage of sales at Amazon was less severe, falling from 43% to 38%, while trade paperbacks lost two percentage points. The figures also highlight that despite Amazon’s focus on digital, print books remain crucial to its overall book business.