Perry winning chart battle against Lady Gaga

Katy Perry is on course to outsell Lady Gaga in their US chart battle.

The 28-year-old pop star's new single 'Roar' - which is the first track lifted from her upcoming album 'Prism' - is expected to sell double the amount of Gaga's new single 'Applause' in the United States after they were both released on the same day last week.