Amazon is now selling more Kindle books than print books. It's going to be interesting to see just how successful Apple's iBookStore will be.

Amazon began selling hardcover and paperback books in July 1995. Twelve years later -- in November 2007 -- the company rolled out the Kindle and began selling Kindle books. By July 2010, Kindle book sales had surpassed hardcover book sales, and six months later, Kindle books overtook paperback books to become the most popular format on Amazon.com. Today, less than four years after introducing Kindle books, Amazon.com customers are now purchasing more Kindle books than all print books -- hardcover and paperback -- combined.

Since April 1, for every 100 print books Amazon.com has sold, it has sold 105 Kindle books. This includes sales of hardcover and paperback books by Amazon where there is no Kindle edition. Free Kindle books are excluded. If included that would make the number even higher.

As of March, Apple had sold more than 100 million e-books from Apple’s e-book store, which was launched with the original iPad. iBooks has since expanded to all Apple devices running iOS 4 and above. That same month Random House said it would join Apple’s iBooks offering, bringing more than 17,000 new titles to the store.

Random House had been the last holdout among the six major publishing houses to join the iBookstore. All told, there are now more than 2,500 publishers on the iBookstore.

If Apple's iBook sales continue to grow at a pace similar to Amazon's, it will be another successful gem in Apple's crown. Now if only the e-magazine sales would follow. Perhaps we need an iNewsStand as well as an iBookstore.

-- Dennis Sellers