If i look at the maps http://maps.google.com/ i could see that the concentration of oil in middle east must be a lot higher than for example in us or the north sea. Is there any gelogical reason to believe that middle east has a lot more oil per area than any other area of the world. Then i check these http://www.searchanddiscovery.net/documents/2004/horn/images/13.htm and http://www.searchanddiscovery.net/documents/2004/horn/images/14.htm i could see that middle east are dominated by carbonate. Is it possible that this could create a skewness towards large easy to tap reservoirs that gives the perception that they have lot more oil than they have.

It's possible. Saudi Arabia has (had?) the most productive wells in the world because of the exceptional quality of their reservoirs. That's explains also why they have drilled so little compared to the US for instance.