The United States has spent roughly $100 billion on private contractors in Iraq since the U.S. invaded the country in March 2003, according to a government report.

The report, by the Congressional Budget Office, says “that one out of every five dollars spent on the war in Iraq has gone to contractors for the United States military and other government agencies, in a war zone where employees of private contractors now outnumber American troops,” the Times reported Monday evening.

The CBO report for the first time puts a price tag on the cost of outside contractors. The report underscores the degree to which the Iraq war has been privatized. But experts believe that the federal government actually spent more than $100 billion on contractors since the war began.

Author and contracting fraud expert Dina L. Rasor told the Times that the $100 billion cost estimate from the Congressional Budget Office appeared to be low because of the lack of audits and controls on spending during the first few years of the war.

“It is a shocking number, but I still don’t think it is the full cost,” Rasor told the Times. “I don’t think there have been any credible cost numbers for the Iraq war. There was so much money spent at the beginning of the war, and nobody knows where it went.”

The Department of Defense’s dependence on independent contractors surpasses all previous military conflicts and has led to “overbilling, fraud and shoddy and unsafe work that has endangered and even killed American troops,” according to the Times.

“The budget office’s report found that from 2003 to 2007, the government awarded contracts in Iraq worth about $85 billion, and that the administration was now awarding contracts at a rate of $15 billion to $20 billion a year. At that pace, contracting costs will surge past the $100 billion mark before the end of the year. Through 2007, spending on outside contractors accounted for 20 percent of the total costs of the war, the budget office found, according to the people with knowledge of the report,” the Times report says.

The occupation of Iraq employs nearly 200,000 people in what amounts to an army larger than the U.S. military force deployed there and “one whose roles and missions and even casualties among its work force have largely been hidden from public view.”