Shares of Amazon (NASDAQ:AMZN) fell in after-hours trading on Thursday, after the e-commerce giant reported fourth-quarter earnings that left a lot to be desired. For the quarter ended Dec. 31, 2013, Amazon generated net sales of $25.59 billion, which was a 20% spike over the same period a year ago. This number was in the mid-range of Amazon's guidance. Nevertheless, it was below analyst estimates for fourth-quarter revenue of $26 billion.

Amazon posted a profit of $239 million for earnings of $0.51 per share, up from $0.21 in the year-ago period. However, that, too, missed the analysts' mark, as the Street was looking for earnings per share of $0.66 in the quarter. Despite coming in below estimates with its fourth-quarter results, Amazon achieved many milestones in the past year. The company's Amazon Prime service celebrated a record-setting holiday season, with its Prime service now boasting "tens of millions of members worldwide."

In a letter to investors, Amazon's CEO Jeff Bezos said: "It's a good time to be an Amazon customer. You can now read your Kindle gate-to-gate, get instant on-device tech support via our revolutionary Mayday button, and have packages delivered to your door even on Sundays."

For its full-year fiscal 2013, Amazon generated net sales of $74.45 billion, which was up 22% year over year. The stock was down more than 7% as of 5:18 p.m. on Thursday.

Tamara Rutter owns shares of Amazon.com. The Motley Fool recommends Amazon.com. The Motley Fool owns shares of Amazon.com. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.