Black tea has the most caffeine among traditional teas (48 mg/8 oz cup), but the actual content varies. Green tea has less caffeine (28.8 mg/8 oz), while herbal teas are caffeine-free unless they contain mate or yerba mate.Black tea has the most caffeine among traditional teas (48 mg/8 oz cup), but the actual content varies. Green tea has less caffeine (28.8 mg/8 oz), while herbal teas are caffeine-free unless they contain mate or yerba mate.