Research firm IDC says Google’s Android operating system has extended its dominance in the smartphone market largely because of the success of Samsung’s line of phones that run the software.

IDC says Samsung Electronics Co. and other phone makers shipped nearly 105 million Android smartphones in the second quarter. Android had 68 percent of the worldwide market, up from 47 percent a year earlier.

The gains come largely at the expense of BlackBerry phones made by Research in Motion Ltd. and Symbian phones used mostly by Nokia Corp. Each saw its market share drop below 5 percent.

The market share for Apple Inc.’s iPhone fell slightly to 17 percent, but the company shipped more units than a year ago. Apple is the No. 2 smartphone maker, behind Samsung.