下麵的這個說法大概是比較科學的（轉）

You cannot generalize about caffeine content by tea type. Many tea companies, and even some reputable entities such as the U.S. Department of Agriculture, have made misleading generalizations about the caffeine content of broad classes of tea. It is a widespread myth that black tea contains more caffeine than green tea, and another myth that white tea contains the least caffeine of all teas.

Studies that have actually measured the caffeine content of a large number of different teas have consistently found that caffeine levels vary more among individual teas than across broad categories of tea such as black, white, green, oolong, or pu-erh. A study published in 2005 in the Journal of Food Science listed, among other things, the caffeine content of 77 different teas, and found a broad range of caffeine content among both green and black teas.[4] Surprisingly, the tea in this study that was found to contain the most caffeine was a white tea, solidly dispelling the myth about white tea's caffeine content.

A more recent study in the 2008 Journal of Analytical Toxicology examined the caffeine contents of a number of teas, and found that they ranged from 14 to 61 mg per 6 or 8 oz serving, with "no observable trend in caffeine concentration due to the variety of tea".[5] Few tea companies have examined the caffeine content of a large number of samples of their teas; one that has, Camellia Sinensis Tea House, found similar results, that the caffeine level varies widely from one tea to the next, and does not show clear trends of caffeine levels across different varieties of teas.[6]

One possible exception to this observation is that matcha is known to contain high levels of caffeine, consistently much higher than other teas. This is due in part to higher caffeine levels in the leaf used to produced matcha, but it is also due to the fact that, because matcha is a powdered tea, the entire tea leaf is consumed when brewing, so a cup of prepared matcha contains 100% of the caffeine in the leaf.