• by Mark Walsh  @markfwal, September 2, 2011

Story after story this year has charted the remarkable expansion of Android to become the world's largest smartphone operating system. In the second quarter, Android accounted for 48% of smartphones shipped -- with Apple's iPhone a distant second at 19%, according to an estimate from research firm Canalys.

But when it comes to mobile browsers, Apple's Safari remains easily the most pervasive. New findings from  NetApplications show Safari with a wide and as-yet unchallenged lead over rivals, including the browser within Android.

Mobile Safari is used by more than half (53%) of browsing done on mobile devices as of August -- a level it has maintained fairly consistently going back to last year, according to the NetApplications data.

Indeed, its browser share has increased from 44.3% in October 2010. Safari's gains have come at the expense of Opera Mini, the No. 2 mobile browser, which has seen its share slip from 30% last October to 20% in August.

Also grabbing share from Opera Mini is the Android browser, which has risen from 10% to 16% of the mobile browser market in the last year. Noting that Opera Mini has typically targeted non-smartphone mobile devices, GigaOm's Darrell Etherington suggested that fact might have accounted for its early success, as well as its slow decline as people upgrade from feature phones to smartphones.

It would not be surprising to see the Android browser overtake Opera Mini in the coming year, if not months.

Still, a key factor boosting Safari and providing a decisive edge over Android is the iPad. Despite the Android OS surging past Apple's iOS platform when it comes to smartphones, Android tablets have hardly made a dent in the iPad's market share, estimated at about 85%. In its most recent quarter, Apple sold 9.25 million of the tablets, a 183% increase from the year-earlier period.

The NetApplications data also roughly corresponds with findings from mobile ad network Millennial Media showing that iOS still generates a larger share of in-app ad revenue than Android, partly because of the iPad's dominance in the tablet space.

A separate study earlier this year by mobile ad exchange Mobclix also found that iOS was significantly more effective than Android in yielding revenue from in-app ads, making Apple device users more "valuable" to developers and advertisers.