Costco Wholesale reported a 6 percent rise in June same-store sales that beat analysts' estimates, helped by higher fuel prices.
Excluding the impact of foreign exchange rates and gasoline prices, same-store sales rose 6 percent for the five-week period ended July 6.
Analysts expected same-store sales to rise 5.4 percent for the month of June, according to Thomson Reuters data.
Costco, which competes with BJ's Wholesale Club and Wal-Mart's Sam's Club, offers everyday items such as bananas below supermarket prices, hoping customers will buy other goods as well and usually prices gasoline lower than competing stations.
June net sales rose 10 percent to $10.89 billion.