Oil shale and Kerogen (which is what we need to extract) are two different things. We have a lot of oil shale in the US but with extremely low levels of Kerogen. The petroleum company BP calculates that worldwide there is about 1200 billion barrels of recoverable petroleum and only 620 billion barrels of recoverable Kerogen (sources:
http://en.wikipedia.org/wiki/Oil_shale and the BP Statistical Review of World Energy, 2006).
Note that "recoverable" is a misnomer; getting the first half (roughly) of any deposit out of the ground is straightforward. After that point the cost/benefit ratio goes up dramatically.
The lift cost (the cost of removing the oil or shale from the ground) is also dramatically different. Saudi Arabia has a lift cost of approximately $1.50 per barrel. Iraq is actually a bit less at around $1.00 per barrel. Every other country is higher. The process of removing Kerogen requires roughly 1 barrel of energy for each 3 barrels recovered. Plus there are other factors (extremely large water requirements; processing the shale to extract the Kerogen; refining it into useful components; considerable environmental problems, etc.). Since there hasn't been a successful commercial demonstration of this process in the US it isn't possible to know how costly the process will be or at what rate this can be extracted from the ground.
New Oil discovery found in Gulf of Mexico
