The USGS has a long history of producing inflated estimates of available oil. This is an article by David Strahan about this problem.

The USGS’s reputation goes back a long way. When the Shell geologist M. King Hubbert published his now legendary paper in April 1956, with its startling prediction that American oil production would peak and start to fall within 15 years, the Survey’s Deputy Chief Geologist Vincent McKelvey was among those who tried to discredit the forecast by promoting an estimate of the US oil resource that was almost three times higher than the biggest number used by Hubbert. This mattered because the central hypothesis of Hubbert’s work was that oil production tends to go into terminal decline at about the midpoint of depletion, when half the oil that will ever be produced from a given region is still underground. So the bigger the resource estimate, the longer the peak would be deferred. As I describe in The Last Oil Shock, this may have been McKelvey’s aim.

My impression is that their view of what is available is generally trending higher. At one point, I had a link to some data showing the figures over time - I don't see it right now.