Casual clothing giant Gap Inc on Thursday posted a 13 per cent jump in September same-store sales on the back of a strong performance from all of its brands.

The California-based operator of more than 4,200 stores added total sales for the five weeks ended October 4 rose 14 per cent to $1.5 billion from $1.3bn in the same period of last year.

The company said same-store sales at its Gap US division soared 13 per cent with comparable sales at Gap International up three per cent, up 12 per cent at Banana Republic and 16 per cent at Old Navy.

"September was a strong domestic month, with each brand posting double-digit positive sales comps and positive store traffic comps," said Sabrina Simmons, senior vice president, treasury and investor relations.

"Advertised products at each brand, such as Gap's stretch pants for women and the relaxed boot fit jean for men, performed well. Overall, total company sales exceeded beginning-of-month expectations and merchandise margins improved over last year."

She added year-to-date same-store sales were up 10 per cent while total year-to-date total sales were up 13 per cent to of $9.7bn from $8.6bn in 2002.