In order of decreasing share of world's proven oil reserves, with R/P ratio indicating the time until reserves are depleted:

24.9 % - Saudi Arabia (R/P = 85 years left)
10.7 % - Iraq (R/P = ??? unknown)
9.3 % - United Arab Emirates (R/P = ??? unknown)
9.2 % - Kuwait (R/P = ??? unknown)
8.5 % - Iran (R/P = 67.4)
7.4 % - Venezuela (R/P = 63.5 years left)
4.6 % - Russian Federation (R/P = 19.1 years left)
2.9 % - USA (R/P = 10.7 years left)
2.8 % - Lybia (R/P = 57.3 years left)
2.6 % - Mexico (R/P = 21.7 years left)
2.3 % - China (R/P = 19.9 years left)
2.3 % - Nigeria (R/P = 30.8 years left)
1.4 % - Quatar (R/P = 55.5 years left)
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89.0 % - Total World Proven Oil Reserves

World R/P = 40.3 years remaining until depletion

(all other countries less than 1% each)

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DEFINITIONS:
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Proved reserves of oil - Generally taken to be those quantities that geological and engineering information indicates with reasonable certainty can be recovered in the future from known reserves under existing conditions.

Reserves/Production (R/P) ratio – If the reserves remaining at the end of any year are divided by the production in that year, the result is the length of time that those remaining reserves would last if production were to continue at that level.

Source of data - With the exception of Azerbaijan and Kazakhstan, the estimates contained in this table are those published by the Oil and Gas Journal, plus an estimate of natural gas liquids for USA and Canada. Reserves of shale oil and oil sands are not included.

BP Statistical Review of World Energy 2002

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My Opinion
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The R/P ratio assumes that oil production will remain constant. However that has not been the trend historically and up until now, and indeed most governments predict steady increases in the future. If we assume free trade exists between all countries and each has unlimited capability to increase production and exports of oil to whomever needs it, then my prediction for world oil depletion is just 29 years. This is the "Brick Wall" when all oil production stops.

However we know that the "Brick Wall" will never happen, as shown by the bell-curve production characteristic demonstrated by oilfields in the USA and the North Sea. Production will hit a so-called Hubbert Peak many years before fully depleting the reserves, after which no matter how hard we try, no matter how many oil wells we drill, we will not be able to increase production. Then as we continue to consume oil, the output from the oilfields will begin an exponential and eternal decline towards zero, although never quite reaching it, and sending the cost of oil into the stratosphere.

Oil production equipment, designed for and installed during peak production, will be working ever further below capacity, never quite paying for itself, and eventually the companies that invested in that capital equipment will go bankrupt as their annual revenues slip below their maintenance expenses, and their profits go negative. Citizens who bought cars that run on petroleum, and are not equipped for Flexible Fuelling, will have to park their vehicles and never drive them again. Businesses that depend on their gasoline- or diesel-run automobiles will find themselves unable to run their company.

So in theory we will never run out of oil, and as production starts failing, and the price of fuel soars worldwide, oil companies will, much to everyone's frustration, be reporting hundreds of millions of barrels of oil reserves still remaining.

And the countries with the largest oil reserves will be hostile (see list above), with wars being waged to overthrow their governments, to install trade-friendly governments, justified via some idealogical fantasy (they're developing WMD, their children are starving, they are ruled by a corrupt regime, or some such nonsense).