LOS ANGELES, June 10 (Xinhua) -- Warner Bros' "Ocean's Thirteen" was on track to sell the most tickets at theaters in North America this weekend, with an estimated 37.1 million dollars in sales over the three-day period, according to box office tracking firm Media By Numbers Sunday.

    Another third version of a previously-successful movie franchise stole the opening weekend box office crown, showing the third time is truly the charm in Hollywood this summer, when blockbuster sequels have helped produce the biggest collective box office revenue in the industry's history.

    The third version of the George Clooney-Brad Pitt series opened this weekend to strong sales. The film was reportedly averaging over 10,000 dollars in each of the 3565 theaters across the United States and Canada.

    "Ocean's Thirteen" is the fourth "Chapter 3" picture in a row to debut at number one this summer after "Spider-Man 3," "Shrek the Third" and "Pirates of the Caribbean: At World's End" respectively claimed the title last month.

    Disney's third installment of "Pirates of the Caribbean" franchise, in its third week of release, showed staying power and cinched second place at box office with an estimated 21.3 million dollars in sales. It edged out the Universal comedy "Knocked Up," which held up strongly in its second weekend with 20 million dollars.

    Sony's new release "Surf's Up", a family animated comedy about surfing penguins, debuted with 18 million dollars at No.4, while Dreamworks Animation's "Shrek The Third" maintained fifth place at box office by selling 15.8 million dollars in tickets over the weekend.

    Meanwhile, "Spider-Man 3" remains the runaway best seller this summer, with sales of 326 million dollars domestically and 865 million dollar worldwide. The superhero film was at No. 8 this weekend with 4.4 million dollars.

    The top 12 films at North American theaters this weekend took in 133.6 million dollars collectively, down about 9 percent from the same weekend last year, suggesting that Hollywood's red hot start of summer season has begun to cool off.