McDonald’s is selling Monster energy drinks in about 20 U.S. restaurants.

OAK BROOK, ILL. — Monster Beverage may have found a new revenue stream with the news that fast-food chain McDonald’s is selling its energy drinks in about 20 U.S. restaurants in Florida, Georgia, Michigan and Ohio.

“We’re always gathering feedback from customers on the food and beverages they’d like to be served at McDonald’s, and this is another example,” said Lisa McComb, a spokeswoman for McDonald’s.

The news sent shares of Monster Beverage rising on Oct. 20. After closing at $132.70 on Oct. 19, the company’s stock opened at $134 on Oct. 20 and moved as high as $142.49 before closing at $139.61.

In an Oct. 20 research note, Robert Ottenstein, an analyst with Evercore ISI in New York, said Monster may have the potential to add as much as $1.5 billion of incremental revenue if it’s able to break into the quick-service restaurant industry. Monster benefits from its partnership with The Coca-Cola Co., Atlanta, which earlier this year bought about a 17% stake in Corona, Calif.-based Monster. McDonald’s also has a long-standing relationship with Coca-Cola.

Mr. Ottenstein wrote that early results from the Monster test have been characterized as “good.” He said most sales are part of a value meal, with consumers paying about $1.50 more to get the Monster drink. If not part of a value meal, the beverages — Original Monster Energy “Green” and Zero Ultra — are selling for $2.50 a can or $4 for two cans, he said.

Mr. Ottenstein said the test is “generating incremental revenue and traffic for stores with some customers coming in just to purchase Monster.” He added Monster sales have cannibalized some trademark Coca-Cola sales, and strongest demand appears to be evenings and late night.

The beverage will not be offered as a fountain drink, though, because of “portion control issues,” Mr. Ottenstein said.

In offering Monster beverages, McDonald’s is continuing to search for ways to turn around a business that has struggled in the United States. The company earlier this month began offering all-day breakfast.