Specialty clothing retailer Gap Inc has booked an 8% rise in sales for the second quarter, boosted by increases at Old Navy and its namesake brand.

The San Francisco-based retailer, which operates around 3,100 stores, said net sales reached US$3.87bn for the three months to 3 August, up from $3.58bn in the same period last year.

Comparable store sales rose 5%, with a 6% increase at both Gap and Old Navy, while Banana Republic posted a 1% decline.

"We are pleased with our second quarter performance overall, and we're focused on continuing our momentum as we move into the second half of the year," said chairman and CEO Glenn Murphy.

In July, total sales grew 5.7% to $1.12bn from $1.06bn the prior year. Comparable store sales edged up 1%, helped by a 7% gain at Gap, which offset a 5% decline at Old Navy and a 1% drop at Banana Republic.

Looking forward, the company expects second quarter earnings per share to be in the range of $0.62-0.64, up from $0.49 in the same period last year.