I just did a bunch of research on the subject and came up with these conclusions:
Nobody really knows how much oil anyone has access to. Why? Because for some it's profitable to keep the info secret, in other cases certain areas haven't been prospected and in others we don't have the means to get an accurate prediction. Also, "oil reserves" are not gauges of how much actually exists, but what can be had at an efficient cost.
The United States has the largest known concentration of oil shale in the world, according to the Bureau of Land Management and holds an estimated 800 gigabarrels of recoverable oil, enough to meet U.S. demand for oil at current levels for 110 years.
Saudi Arabia: 700 billion bbl current known potential, 900 billion projected potential by 2025 as the Rub' al Khali desert region, the northern basin (along the border with Iraq) and the offshore Red Sea Basin do not have a potential projection yet.
Canada: Doesn't have much oil, but has a lot of stuff which can be used nearly the same as oil. 1.8 trillion bbl potential.
Russia: Probably has the most. They don't share much info.
Oil reserves refer to portions of oil in place that are recoverable under economic constraints. In comparison, oil in place, or STOOIP, meaning "Stock Tank Oil Original In Place", represents all of the liquid hydrocarbon contained in a reservoir.
Oil in the ground is not a reserve unless it is economically recoverable, since as the oil is extracted, the cost of recovery increases incrementally. The recovery factor (RF) is the percentage of STOOIP which is economically recoverable under a given set of conditions.
Reserves = STOOIP * RF
Proven, probable and possible reserves are the three most common categories of reserves. They represent the certainty that a reserve exists based on the geologic and engineering data and interpretation for a given location.
* Proven Reserves - defined as oil and gas "Reasonably Certain" to be producible using current technology at current prices, with current commercial terms and government consent- also known in the industry as 1P. Some Industry specialists refer to this as P90 - i.e having a 90 % certainty of being produced
* Probable Reserves - defined as oil and gas "Reasonably Probable" of being produced using current or likely technology at current prices, with current commercial terms and government consent - Some Industry specialists refer to this as P50 - i.e having a 50 % certainty of being produced. - This is also known in the industry as 2P or Proven plus probable
* Possible Reserves - i.e "having a chance of being developed under favorable circumstances" - Some Industry specialists refer to this as P10 - i.e having a 10 % certainty of being produced. - This is also known in the industry as 3P or Proven plus probable plus possible
http://www.radford.edu/~wkovarik/oil/3u ... ional.html