Amazon announced impressive earnings in its third quarter, thanks to the growing popularity of online shopping and the acquisition of Zappos.

The e-commerce behemoth’s revenue increased 39 percent to $7.56 billion in the third quarter, compared with $5.45 billion in third quarter 2009. Operating cash flow increased 16 percent to $2.62 billion for the trailing 12 months, compared with $2.25 billion last year.

Net income increased to $231 million in the third quarter, or $0.51 per diluted share, compared with net income of $199 million, or $0.45 per diluted share, in third quarter 2009.

"Every year for the last 15 years we've worked to improve the things customers care about, and this year is no exception," said Jeff Bezos, founder and CEO of Amazon.com, in a statement. "This holiday season we'll have the best prices, the biggest selection, the highest in-stock, and the fastest delivery in our history."

Amazon also appears to be making headway both domestically and internationally. North America segment sales, representing the company's U.S. and Canadian sites, were $4.13 billion, up 45 percent from third quarter 2009. International sales, representing the U.K., Germany, Japanese, French and Chinese sites, were $3.43 billion, up 32 percent from third quarter 2009.

Amazon’s purchase of Zappos appears to be paying off. In July 2009, Amazon bought the popular startup for 10 million Amazon shares or $880 million. In an open letter, Zappos CEO Tony Hsieh broke the news to its employees:

“We plan to continue to run Zappos the way we have always run Zappos -- continuing to do what we believe is best for our brand, our culture, and our business. From a practical point of view, it will be as if we are switching out our current shareholders and board of directors for a new one, even though the technical legal structure may be different.”