Iraq is looking at a potential boon in oil revenue this year, as the U.S. spends some $153 million a month in the country on fuel alone. But U.S. officials say it will take some time before Baghdad builds the capacity to manage the revenue.

The money isn't "just sitting in banks trying to get somebody rich on interest income," said Adm. William Fallon, who recently stepped down as the top U.S. military commander in the Middle East. "It's because they're in a holding position now until they can figure out how to effectively disburse these moneys."

Stuart Bowen, special inspector general for Iraq reconstruction, said Baghdad in recent months has experienced its highest oil production and export levels since the war began five years ago.

Whereas Iraqi officials estimated $35 billion in oil revenue last fall, Bowen said the final number is likely to be closer to $60 billion.

Sens. Carl Levin, D-Mich., and John Warner, R-Va., have called for an investigation into Iraq's handling of the money. While Iraq pays for fuel for its own troops, it relies heavily on U.S. dollars to provide citizens with basic services, including more than $45 billion for reconstruction.

"We believe that it has been overwhelmingly U.S. taxpayer money that has funded Iraq reconstruction over the last five years, despite Iraq earning billions of dollars in oil revenue over that time period that have ended up in non-Iraqi banks," Levin and Warner wrote in a letter to the head of the Government Accountability Office.

"At the same time, our conversations with both Iraqis and Americans during our frequent visits to Iraq, as well as official government and unofficial media reports, have convinced us that the Iraqi government is not doing nearly enough to provide essential services and improve the quality of life of its citizens," they said.

The senators estimated that Iraq will realize "at least $100 billion in oil revenues in 2007 and 2008."

But administration and military officials say it's not that easy to distribute the money. They contend that Iraq's lack of spending isn't due to laziness or corruption, but rather Baghdad's inability to determine where its money is needed most and how to allocate it efficiently.

The Iraqis have a "genuine mechanical problem in drawing up national budgets (and) executing those budgets, particularly when it comes to capital infrastructure," said David Satterfield, the State Department's senior adviser on Iraq.

Iraq's Oil Ministry in 2006, for example, spent only a fraction of its capital budget, he said.

"It wasn't a security reason. It wasn't a political reason. It wasn't a question of corruption. It was an issue of simply a lack of experience in how you go about doing capital investment," Satterfield said. "Iraq is a country, you have to recall, in which virtually no capital infrastructure investment had been made for decades."

Satterfield and other officials say the situation is improving.

The Defense Energy Support Center, which acts as the military's primary broker for fuel, provides troops in Iraq with about 1.2 million barrels of fuel per month at $127.68 a barrel, a price that reflects crude oil refined into usable fuel.