In an article in Food research International, Vol 29, 325-330 (1996), the content of caffeine in various teas and _style_s of brew were compared.

One of the formosa oolongs had less caffeine than the green and black teas on a dry weight basis, but when all were prepared to supplied directions, they had similar caffeine levels. When brewed for a series of three repeated brews, the caffeine concentration was higher in the first brew for one of the other Formosa oolongs than other green, black, and oolong teas. The caffeine content decreased dramatically from the first to the third brew, about 50-70mg/cup in first cup, 15-25 in second, and 5-10 in third, each brew about 5 minutes in length.