Here is a sortable table of caffeine amounts in products. The numbers are quite striking.
http://www.energyfiend.com/the-caffeine-database
For example (mg caff / oz):
Red Bull = 80 / 8.46
Rockstar = 160 / 16
Coca Cola = 35 / 12
Fixx Energy = 400 / .17
I haven't drank Red Bull in a few years so things may have changed.
I checked the amounts of caffeine and other "medicinal" ingredients myself when I was doing physical labour and drank them regularly.
http://www.reuters.com/article/healthNews/idUSSYD58461200808...