Oh, my! Lets put the major oil companies in perspective with respect to reserves.
1. Exxon-Mobil buys 90% of the oil that it refines for the U. S. market. Moreover, the amount of refined oil that it buys is growing as the nations with the oil reserves build large refineries to add to their profits.

On the internet is a chart from Chevron Oil, printed by Credit Suisse First Boston, and lifted by a blogger- it is important information.
It shows just how small and weak the majors like Exxon, Shell, Chevron, Total, BP, etc., are.

2. Oil reserves, 'proven,' my figures approx. since I eye-balled them from the graph. (Gas is liquified conversion) B = billion bbls

NIOC (Iran) Oil- 130 B, Gas- 200 B
Saudi Arabia Oil- 180 B, Gas- 40B
Gazprom (Russia) Oil- 30 B, Gas 150 B
Qatar Oil- 30 B, Gas 150 B
ADNOC (UAE) Oil- 100 B, Gas 50 B
Iraq Oil- 120 B, G 10 B
KPC (Kuwait) Oil- 90 B, G 40 B
PDVSA (Venezuela) Oil- 80 B, G- 50 B
NNPC (Nigeria) Oil- 45 B, G- 40 B
NOC (Lybia) Oil- 50 B, Gas 15 B
Sonotrach (Algeria) Oil- 20 B, Gas- 30 B
Rosnof (Russia) Oil- 20 B, Gas 25 B
Petronas (Malaysia) Oil- 10 B, Gas 20 B
EXXON MOBIL Oil- 20 B, Gas 15 B (Exxon says 22.7 B Oil)
Petrochina (China) Oil- 20 B, Gas 10 B

Exxon Mobil is in 14th place- their reserves are tiny compared to the reserves controlled by state owned companies- some 90%- and NO WAY can the American or European majors buy those reserves below market.

BP has about the same amount of reserves as Exxon Mobil, Shell, Total and Chevron somewhat less.

Note- I think the Iran data are inflated, esp. the gas estimate.

Canada, the No. 1 source for U. S. oil, does not appear since the oil sands are mined, and liquid reserves are small.

http://www.powerlineblog.com/OilChart9.jpg