LOS ANGELES — Which is more powerful: Superman or Walmart?

In an unusual promotional partnership that starts on May 18, customers at 3,718 Walmart stores in the United States will be able to buy tickets to early screenings of “Man of Steel,” the coming Superman movie from Warner Brothers.

About one million tickets will be put aside. Sellouts are expected. Prices will vary but will generally stay in line with the cost of tickets at the local theaters.

The promotion is designed to fill seats on opening weekend; Warner is counting on extensive in-store advertising and a burst of chatter on social media. Simultaneously, the goal is to send shoppers cascading into the arms of the world’s largest retailer. Warner and Walmart billed the partnership as a Hollywood first.