Have you read and understood the methodology of the USGS report? That would probably be the best place to start.

I have looked at the USGS figures very closely, and no one as yet has produced any good evidence to show they are wrong. In countries where active efforts are being made to discover oil, the volumes being discovered are in line with USGS estimates. In general, the countries which are not performing up to USGS estimates are not discovering new oil because no one has been exploring for oil there. Iraq is the classic example. The USGS estimates that large volumes of undiscovered oil are present in Iraq, but the poor discovery record in Iraq doesn't prove that the oil is not there. No one is drilling because the country is at war.

To prove that the USGS estimates of undiscovered oil are wrong, you need to identify a country/province X satisfying TWO criteria:
 1) Discoveries in X are substantially lower than the USGS estimates suggest
 2) Actual efforts are being made in X to discover new oil.

So far, no one has met the challenge of identifying such a country.

The USGS has a evaluated its own track record, in a paper referenced here.  The USGS procedure for estimating reserve growth has an excellent track record, and in fact has underestimated reserve growth thus far, as you can see in the paper.

If you're curious, there's lots more analysis of the USGS available here