The NPD Group has published research showing that Android continues to lead the mobile OS market in America. The data indicates that Android phones represented 52 per cent of units sold in the second quarter of 2011. This shows significant growth over the 36 per cent first quarter market share indicated in a report by Gartner in May. Apple's iOS grew marginally to 29 per cent, while Blackberry tumbled to 11 per cent, and Windows Phone 7, Windows Mobile and webOS remained stagnant with 5 per cent each. Ross Rubin, NPD's executive director of industry analysis, claims that Google's recent $12.5 billionacquisition of Motorola has "shifted the balance of power" in the patent battle currently playing out in the mobile OS market. "Android's momentum has made for a large pie that is attractive to Motorola's Android rivals, even if they must compete with their operating system developer," he said. "Much as it did in the feature phone market in the RAZR era, Motorola is experiencing increased competition from Samsung and LG in the smartphone market. Closer ties to the heart of Android can help inspire new paths to differentiation." The report also suggests the burgeoning pre-paid smartphone market as a possible area for Android to grow even further. "This was once a key segment for Motorola that the company has an opportunity to reclaim as prepaid carriers build their smartphone portfolios," Rubin said.