How long will the total oil in US and territorial waters last?

The US has about 30 Billion barrels of proven oil reserves. If assume use no oil imports (US imports about 60% of use currently) and current rate of consumption (oil use in US has recently begun to go down) of about 20.7 Million Barrels a day - US oil proven reserves will be drained in about 4 years. If use current levels of import, the current reserves will last about 10 years. If add in estimated prospective oil reserves, the US has about 130 Billion Barrels (unproven) additional reserves. Of the 130 Billion Barrels, ~ 85 BBls are offshore (~20 BBls in currently off limits areas) and ~45 BBls under land (~10 BBls are in ANWR). The prospective reserves would last at current consumption levels about another 17 years (21 total) with no imports or about another 43 years (53 total) at current import levels. The US also has the largest formation of oil shale in the world, with an estimated 1.5 (some estimates are over 2) Trillion barrels of oil in oil shale in reserve or about twice the reserves of the entire middle east, but this oil is harder to get. If use 1.5 TBls with no imports, US has oil to last 200 years at current consumption with no imports and nearly 500 years if assume current import levels just from this source.