Energy drink labels do not always divulge how much caffeine the beverages contain, and when an amount is listed, it is not always accurate, Consumer Reports has found. According to a study released last week by the magazine, 11 of the 27 top-selling energy drinks in the United States do not specify the amount of caffeine in their beverages.

Of the 16 drinks that did list a specific caffeine amount, five had more caffeine per serving than was listed, with the average excess being more than 20 percent.

“There is no legal or commercial business requirement” for beverage companies to reveal exact caffeine levels, a Monster official told Consumer Reports. “And because our products are completely safe, the actual numbers are not meaningful to most consumers.”

Caffeine levels in the drinks tested ranged from about six milligrams per serving for 5-Hour Energy Decaf, made by Living Essentials, to 242 milligrams for 5-Hour Energy Extra Strength, the report found.

The drinks that Consumer Reports found that contained more caffeine than was listed on their labels included Arizona Energy, Clif Shot Turbo Energy Gel, Sambazon Organic Amazon Energy, Venom Energy and Nestle Jamba.

One sample of Archer Farms Energy Drink Juice Infused beverage had about 70 percent less caffeine than advertised, the report found. Archer Farms is the private label of Target.