Worldwide tablet shipments reached 27 million units during the fourth quarter of 2011, according to new research issued by consulting firm Strategy Analytics. While Apple's iOS mobile operating system continues to trounce the competition at 58 percent global tablet market share, Google's Android is closing the gap and now represents a record 39 percent of the market, up from 29 percent a year earlier.

Android tablet shipments tripled annually to 10.5 million units, Strategy Analytics notes. "Dozens of Android models distributed across multiple countries by numerous brands such as Amazon, Samsung, Asus and others have been driving volumes," said Strategy Analytics executive director Neil Mawston in a statement. "Android is so far proving relatively popular with tablet manufacturers despite nagging concerns about fragmentation of Android's operating system, user-interface and app store ecosystem."

Total tablet shipments reached 66.9 million units in full-year 2011, increasing 260 percent from 18.6 million in 2010. Shipments scaled an all-time peak of 26.8 million units in the fourth quarter, up 150 percent from 10.7 million in the year-ago quarter. Apple led the way, shipping 15.4 million iPad units across the globe. At the opposite end of the spectrum, shipments of Microsoft-powered Windows tablets stalled at 500,000 units, making up just 1.5 percent of the worldwide tablet market.  

Strategy Analytics' definition of tablet does not include e-readers.