) reported a 6% gain in May same-store sales. Costco's US same-store sales gained 6%, while international same-store sales jumped 4%. Analysts were projecting a 4.6% increase in same-store sales. Its net sales climbed 8% to $8.78 billion in May from $8.13 billion. Excluding the impact of foreign currencies and gasoline prices, Costco's same-store sales climbed 6%. Costco also announced its plans to open 6 new warehouses before the end of its fiscal year on August 31, 2014. Costco shares gained 0.69% to close at $116.31 yesterday.