NEW YORK (MainStreet) – Less than four years after bringing e-books to the mainstream with the Kindle e-reader, Amazon (Stock Quote: AMZN) has announced that it now sells more Kindle books than print books.

The online retail giant said Thursay that it has sold 105 Kindle books for every 100 print books sold on its site since April 1 of this year. According to the company, that shift has come as a result of an explosion in e-book sales, and it also added that Kindle book sales have tripled year-over-year so far in 2011.

While it’s amazing to see how far e-books have come in recent years, it’s not surprising. The Kindle in particular has come down in price considerably of late, due in part to competition from rival e-readers like the Barnes & Noble Nook and tablet computers like Apple’s iPad. The first generation Kindle debuted at a $399 price point in 2007; today the baseline model sells for $139, and readers willing to look at some ads can get it for as cheap as $114. (Amazon said this cheap version is already the best-selling version of the Kindle.)

Amazon isn’t the only retailer seeing huge sales of e-books. Barnes & Noble (Stock Quote: BKS) announced in December that sales of Nook e-books had likewise passed sales of print books on its own site, BN.com.

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