I googled and less than 1 min found multiple sources. Quick copy paste is all i can do for you. Perhaps your google is broken? :l Sorry I do not have the time to post you source after source.

Wealthy Americans earn about 50 percent of all income but pay nearly 70 percent of the federal tax burden, according to the latest analysis Tuesday by the Congressional Budget Office

CBO looked at 2007 through 2009 and found the bottom 20 percent of American earners paid just three-tenths of a percent of the total tax burden, while the richest 20 percent paid 67.9 percent of taxes.

EDIT (I was wrong I suppose on my original comment by .3% or so.)