Worldwide shipments of tablet computers failed to meet forecasts in the third quarter of 2011 despite a 23.9 percent increase compared to the previous quarter. IDC’s Worldwide Quarterly Media Tablet and eReader Tracker found that tablet shipments reached 18.1 milion units during the period – 265 percent up on the same quarter in 2010, but below the 19.2 million units forecast by IDC.

However, IDC foresees strong demand for tablets in the current quarter, raising its worldwide shipment forecast for 2011 to 63.3 million units from 62.5 million.

Apple shipped 11.1 million iPads in the third quarter, up 1.8 million units from Q2 and representing 61.5 percent of the total market. The market share was a little down from the 63.3 percent seen in the previous quarter. Samsung was second in terms of shipments with 5.6 percent of the market while HP secured a 5 percent market share by shipping 903,354 TouchPads after slashing the price of the device.

IDC added LCD-based devices to the media tablet category during the period, meaning Barnes & Noble hit fourth spot with a 4.5 percent market share after shipping 805,458 Nook Colors. Asus was fifth with a 4 percent share.

Android-powered devices lost ground slightly in terms of market share – falling from 33.2 percent to 32.4 percent – but IDC expects a significant share gain in the fourth quarter due to the introduction of Amazon’s Kindle Fire and the Barnes & Noble Nook Tablet. The analyst firm expects Android devices to secure a 40.3 percent market share during the period.

"Apple's larger portfolio of tablet-specific apps, upcoming iPad versions, and growing physical store presence in key emerging markets like Asia/Pacific will help maintain its global leadership. However, an improving Android OS experience and lower competitor pricing in an environment with worldwide economic concerns should help Android to increase its market share," IDC research analyst Jennifer Song said.

The increase in Android’s market share will come at the expense of RIM’s BlackBerry PlayBook (currently 1.1 percent) and iOS, which is expected to slip to 59 percent.