The online retailer said that since April 1, it has sold 105 e-books for every 100 printed books, including printed books for which there is no electronic edition. The comparison excludes free e-books, which would tip the scales further if they were included.
Printed books include both hardcover and paperback books. Amazon said in July that e-book sales had outstripped hardcover sales. It's now selling three times as many e-books as it did a year ago.
Analysts estimate that Amazon accounts for about two-thirds of U.S. e-book sales.
Amazon also said the latest and cheapest version of its Kindle e-book reading device is the best-seller of the line, five weeks after it was introduced. The Kindle with Special Offers costs $114, and shows ads in standby mode.
