Offshore - Oil Production Zones
The Oil Production Zones of the world tend to be certain regions conducive to the extraction of easy to reach oil. Countries that are producing, that is to say extracting and refining oil are many but generally it is the OPEC countries which hold two thirds of the worlds oil supply that dominate the worlds oil market. Oil which is produced and exported worldwide tends to be directly linked to the oil reserves available. A place with a plentiful amount oil will export that oil it does not need. Thus large oil reserves will mean significant production.
To state which countries have the largest oil reserves can be misleading. Firstly, a country may have vast supply of oil in its territory but not the technological means to extract it to be economically viable. Secondly, the political stability may be in question in a region causing oil extraction to be upset. A classic example is the Bonga Field (Nigeria) in the Niger Delta which has seen kidnapping of oil workers there. Thirdly, there is the proven oil reserves, oil which is known and proven to exist but may require additional capital investment to develope(well drilling, platform development). Fourthly, certain countries have oil shale and oil sands reserves which can be refined into petroleum (expensive process though) this too is often classed as an 'oil reserve.'
Currently Saudi Arabia has the largest in proven oil reserves in the world and produces a record amount of oil last year (2006). The 'House of Saud' is indeed the reigning oil king although some experts believe the future oil story for them and others may change.
The Oil Giants Of The World
Saudi Arabia - 262 Gb
The USA - 22 Gb
*This includes non-conventional oil; mostly tar sands, oil shale etc which is expensive to extract.