Online retailer Amazon.com now sells 105 Kindle e-books for every 100 printed books, it said today.

Sales of the electronic books surpassed hardcover titles in July 2010, and overtook paperbacks six months later, the Seattle-based company said in a statement.

"We had high hopes that this would happen eventually, but we never imagined it would happen this quickly," said Jeff Bezos, Amazon's founder and chief executive.

The retailer started in 1995 as an online bookseller. It has since expanded into thousands of products, selling everything from DVDs to baby clothes. Amazon may have sold more than eight million Kindles last year, accounting for about 5 per cent of sales, according to Benchmark Co.

Amazon does not disclose Kindle sales figures, other than saying it's the company best-selling product.

Bloomberg