With e-books’ share of unit sales rising from 14% for the first nine months of 2011 to 22% for the same period in 2012, the biggest winners among retailers were Amazon and dedicated e-bookstores and digital download sites. According to the most recent data from Bowker Market Research, Amazon’s share of all unit book sales rose to 27% at the end of September 2012 from 21% during the previous year, while the share of e-bookstores and digital audio sites jumped from 1% to 6%. Sites in the e-bookstore category include Apple’s iBookstore, along with a number of smaller sites.

In addition to higher e-book sales, the gains at Amazon resulted from the insolvency of Borders; the defunct chain is listed in the other category and that category’s share of unit sales fell from 21% in 2011 (which includes Borders) to 13% for the first nine months of 2012. Between September 2011 and 2012, Barnes & Noble’s share of units slipped from 17% to 16%, although B&N was the only other outlet besides Amazon that had a double-digit share of the market. Independent booksellers’ market share tied with e-bookstores and online sites other than Amazon, at 6% of unit sales through the first nine months of last year.

The gain in market share of e-books in the period came at the expense of the three print categories. Mass market paperback and hardcover each lost three percentage points while trade paperbacks’ share fell two percentage points.

In the third quarter of 2012, e-books’ share of dollar sales was 11%, up from 7% in the third quarter of 2011, while hardcover sales for the period fell to 36% in dollar terms, from 39%, and the share of trade paperbacks declined to 36% from 37%. Mass market paperbacks’ share of dollars stayed even, at 6%.