"United States proven oil reserves declined to a little less than 21 billion barrels (3.3×109 m3) as of 2006 according to the Energy Information Administration, ...
If the United States had to supply its entire demand of 21 million barrels per day (3.3×106 m3/d) without resorting to foreign imports, existing US reserves would last only three years at the current rate of consumption." - link
This does not take into account the worlds larges oil shale fields in Colorado (the highest quality shale in the world) and Wyoming that contain more than 1 TRILLION barrels that could begin production in the next decade (Source: Testimony of Terry O’Connor, Shell Executive, at Republican hearings last week on C-SPAN3).