Apple continued to drive worldwide media tablet shipments in the third quarter, according to the International Data Corp. (IDC) Worldwide Quarterly Media Tablet and eReader Tracker. The company shipped 11.1 million units in the third quarter, up from 9.3 million units over the previous quarter. That represents a 61.5 percent worldwide market share, down from 63.3 percent in Q2 2011.

HP's ill-fated TouchPad entered and left the market in the third quarter. IDC says the company shipped 903,354 units to grab a 5 percent share of the worldwide market, No. 3 behind Samsung's 5.6 percent market share.

After IDC updated its taxonomy to move LCD-based devices such as Barnes & Noble's Nook Color into the media tablet category, Barnes & Noble shipped 805,458 units to achieve the No. 4 spot with a 4.5 percent market share. ASUS rounded out the top five with a 4 percent share.

IDC expects Android to make dramatic share gains in the fourth quarter, growing to 40.3 percent, an increase the firm attributes to the entrance of Amazon's Kindle Fire, and to a lesser extent the Barnes & Noble Nook Tablet. The share increase comes at the expense of BlackBerry's PlayBook, which slipped from 1.1 percent to 0.7 percent. iOS slipped from 61.5 percent to 59.0 percent, and webOS fell from 5 percent to 0 percent.

Despite HP's announcement last week that it would contribute webOS to the open source community, IDC does not believe the operating system will reappear in the media tablet market in any meaningful way going forward.

"Amazon and Barnes & Noble are shaking up the media tablet market, and their success helps prove that there is an appetite for media tablets beyond Apple's iPad," said Tom Mainelli, research director of Mobile Connected Devices at IDC. "That said, I fully expect Apple to have its best-ever quarter in Q4 2011, and in 2012 I think we'll see Apple's product begin to gain more traction outside of the consumer market, specifically with enterprise and education markets."

Worldwide media tablet shipments into sales channels rose by 23.9 percent on a sequential basis in the third calendar quarter of 2011 to 18.1 million units. That's an increase of 264.5 percent from the same quarter last year, but 5.8 percent below the original forecast of 19.2 million units. Despite the slightly lower-than-expected shipments, IDC still sees strong demand in the fourth quarter and has increased its worldwide shipment forecast for 2011 to 63.3 million units, up from a previous projection of 62.5 million units.