Amazon.com, Inc. announced financial results for its fourth quarter ended December 31, 2011.

According to a press release, operating cash flow increased 12% to $3.90 billion for the trailing twelve months, compared with $3.50 billion for the trailing twelve months ended December 31, 2010. Free cash flow decreased 17% to $2.09 billion for the trailing twelve months, compared with $2.52 billion for the trailing twelve months ended December 31, 2010.

Common shares outstanding plus shares underlying stock-based awards totaled 468 million on December 31, 2011, compared with 465 million a year ago.

Net sales increased 35% to $17.43 billion in the fourth quarter, compared with $12.95 billion in fourth quarter 2010. Excluding the $101 million favorable impact from year-over-year changes in foreign exchange rates throughout the quarter, net sales would have grown 34% compared with fourth quarter 2010.

Operating income was $260 million in the fourth quarter, compared with $474 million in fourth quarter 2010. The favorable impact from year-over-year changes in foreign exchange rates throughout the quarter on operating income was $5 million.

Net income decreased 58% to $177 million in the fourth quarter, or $0.38 per diluted share, compared with net income of $416 million, or $0.91 per diluted share, in fourth quarter 2010.