Amazon.com offered discounts on the last Harry Potter novel

The retailer said profits in the three months to 30 September quadrupled to $80m (�39m) with more online sales.

The final book in the boy wizard series, Harry Potter and the Deathly Hallows, became the fastest selling book ever upon its release in July.

But Amazon has said it will not make a profit on the title because it offered steep discounts and free shipping.

"In our view, putting customers first is the only reliable way to create lasting value for shareowners," said Jeff Bezos, founder and chief executive of Amazon.

Revenue rose 41% to $3.26bn from the same quarter last year, helped by the 2.5 million copies sold of the seventh Harry Potter book - Amazon's biggest new product release.

Amazon said it anticipated a record holiday season, with expected sales of between $5.1bn and $5.45bn.

Sales of electronics and general merchandise gained more than those of CDs and DVDs.