Costco's December same-store sales beat analysts' expectations, helped in part by online sales in the United States and Canada.
Sales at stores open at least a year rose 3 percent in the five weeks ended Jan. 5, including the impact of fuel sales and foreign exchange.
(Read more: USholiday sales better than last year: MasterCard)
On that basis, analysts expected same-store sales to rise 1.8 percent for the month of December, according to a Thomson Reuters poll.
December net sales rose 6 percent to $11.53 billion.
(Read more: Bleak Christmas for top UK supermarkets)
Excluding the negative impact of foreign exchange and falling gasoline prices, same-store sales rose 5 percent.
Costco, which competes with BJ's Wholesale Club Inc and Wal-Mart Stores Inc's Sam's Club, offers everyday items like bananas below supermarket prices, hoping customers will buy other goods as well. It usually prices gasoline lower than competing stations.
Follow us on Twitter: @CNBCWorld