It doesn't matter any more how much untapped oil the US, or anyone else has.
We are about to pay, in arrears, for far too many years of far too low oil prices.
It takes, on average, 10 years to develop deep-water discoveries and bring the first few barrels to market.
The cost of exploration is becoming prohibitive, and it's only the new high $/bbl price that makes this very risky business worth the risk.
Extraction of shale and tar sands is very energy and water resource intensive, and deposits tend to be in areas that have poor access to either, especially to water.
The price of drilling rigs has gone through the roof in the past year or so. If you're looking for a good investment, get into companies that specialise in extraction services.
If you want to devellope ANWR, or Bakkan, or the new maybe superfield offshore off Brazil, then it will cost much, much more than it would have done two years ago.