Troubled apparel retail giant Gap Inc on Thursday posted a nine per cent year-on-year slide in May same-store sales - its 26th straight month of tumbling same-store sales. The San Francisco-based operator of more than 4,200 stores, including the Gap, Banana Republic and Old Navy banners, said in a statement that total sales for the month ended June 1 slipped two per cent to $995m from $1 billion in the year-ago period.