Because of the oxidization process that goes into the production of black teas, the caffeine levels present in the leaves tends to depreciate. Compared to other tea types, Chinese black teas have about the same caffeine content as green teas, whereas larger leafed Indian black teas have a slightly higher caffeine content. Both types are significantly less than that in a cup of coffee, containing about half the amount of caffeine altogether.
The actual caffeine content present in a cup of black tea varies upon how long the tea is steeped. The longer the steep time, the more caffeine the tea will contain. Caffeine content will lessen each time tea is re-steeped.