Coscto (NASDAQ:COST) Thursday revealed an 11% jump in December sales, helped by strong international sales led primarily by the wholesaler’s Mexican joint venture.

The Issaquah, Wash-based wholesale chain posted sales for the five weeks ended Jan. 2 of $9.19 billion, improved from $8.26 billion a year ago, helped by a 12% comparable-store gain in international markets. U.S. comparable stores grew 4%.

The results were fueled by its Mexican joint venture, which it started consolidating on Aug. 30, the start of its fiscal 2011 year.