Energy Uncertainty
Anarchy in Iraq and the possible breakup of the country into autonomous regions would severely affect Iraq’s oil exports. In 2005, Iraq produced about 1.9 million barrels per day (MBD) of oil and exported about 1.4 MBD. By June 2006, Iraqi oil production had risen to 2.5 MBD, and it has been on the rise ever since. A U.S. withdrawal would undermine the security of oil pipelines and other facilities and increase the vulnerability of Iraqi oil production to sabotage. The resulting drop in Iraqi oil exports would increase the upward pressure on world oil prices in an already tight oil market. Energy uncertainty would be increased further if Iraq splintered and Iran gained domination over a Shia-dominated rump state in the oil-rich south.

The cited oil export data attempt to support that
a) the US presence has increased the export of oil from Iraq
b) a US withdrawal will cause anarchy and a possible breakup of the country
c) anarchy would decrease production and increase world oil prices
d) avoiding decreased Iraqi oil production is worth our spending $300 million per day.
Our occupation has not increased production, but returned it to pre-invasion levels. From August '98 till our invasion in March '03, Iraq exported an average of 2MBD ( http://www.wtrg.com/oil_graphs/PAPRPIQ.gif ). In the five months after the invasion, exports dropped sharply, but resumed previous levels in October '03.
While oil production and prices are certainly related, recent price fluctuations had nothing to do with the supply of Iraq oil. To suggest that we are in Iraq to protect the world from rising oil prices, and that it is worth our spending $300 million a day of US tax payers' money, is not the kind of argument I'd expect from a well-funded, international think tank. Then again, maybe it is...