Private contractors working in Iraq conduct security operations for high-level officials, aid the U.S. military with weapons systems and help Iraq rebuild.

But hard numbers about the consultant population are difficult to come by because not all companies are registered with either the Iraqi or U.S. governments. Following is some information on contractors in Iraq, based on a variety of sources.

Overview: More than 120,000 private contractors are in Iraq, the majority of these perform reconstruction duties.

An estimated 20,000 contractors do security work. Of these, 6,000 are in armed tactical roles, protecting important installations such as corporate enclaves, U.S. facilities, and the Green Zone in Baghdad and guarding key Iraqi and U.S. officials.

The remaining 100,000 contractors help rebuild oil pipelines, electricity grids and other critical infrastructures.

Before handing over power to the new Iraqi government, the Coalition Provisional Authority established "Memorandum 17," which called for all private security companies operating in Iraq to register by June 1 by the Ministry of Trade and established an oversight committee led by Iraq's Ministry of the Interior.

As of June 21, 37 security companies had registered with the Iraqi Ministry of the Interior. One is awaiting approval, and at least 18 additional security companies are in the process of registering, according to Lawrence Peter, a former CPA official and the director of the Private Security Company Association of Iraq.

Rules Governing Contractors in Iraq: U.S. government contracts worth $50 million or more with private companies must be reported to Congress. The companies also must comply with the U.S. International Traffic in Arms Regulations (ITAR), which regulates the import and export of arms material and services.

But many contracting firms don't register with the government, which makes it hard to get an accurate count of exactly who is doing what in Iraq. For example, of the 60 known private security companies operating in the country, only eight worked directly for the CPA. The rest are subcontracted to provide protection for primary contractors or even other subcontractors. When companies are not contracted directly to the government, they are accountable only to the contractor whom employs them.

Salary: Guards for private security firms can typically earn between $400 and $600 per day. Guards employed by Blackwater, a high-profile American company that guarded former CPA chief Paul Bremer, are sometimes paid up to $1,000 per day. Many companies like KBR offer $80,000 to $100,000 a year salaries; many companies offer more for what they call "hazardous duty."

But life insurance policies for contractors, for example, are not usually as generous as their paychecks, or as solid. When a member of the U.S. military is killed, that man or woman's family is guaranteed life insurance and death benefits.

Number of Contractor Deaths: About 248 civilian contractors of all nationalities working on both military and reconstruction contracts have died in Iraq, according to the most recent estimates. American deaths makes up the most of these deaths by country, reaching almost 40 percent of the total deaths overall.

Private military contractors have suffered an estimated 175 deaths and 900 wounded so far in Iraq -- more than any single U.S. Army division and more than the rest of the coalition combined, according to Peter Singer, an expert on contractors and author of the book, "Corporate Warriors."

At least 203 non-Iraqi contractors have been kidnapped since May 2003, according to benchmarks tracked in "The Iraq Index" by the Brookings Institution. The Iraqi Interior Ministry estimates that about 5,000 Iraqis were kidnapped between December 2003 and May 2005.

Contractor Population: According to Doug Brooks, president of the International Peace Operations Association, the breakdown of contractors and their companies in Iraq is:

-- 50,000 support/logistics contractors, civilians hired by KBR, the Halliburton subsidiary which holds the military's logistical support contract. They work as weathermen, cooks, carpenters, mechanics, etc. Most are from Third World countries and the majority are Filipinos.

-- 20,000 non-Iraqi security contractors. Of these, 5-6,000 are British, American, South African, Russian or European; another 12,000 are from Third World countries, such as Fiji, Colombia, Sri Lanka, and India.

-- 15,000 Iraqi security contractors. Most of these were hired mainly by the British security firm Erinys to guard Iraq's oil infrastructure.

-- 40-70,000 reconstruction contractors. Hired to rebuild Iraq. Some are Iraqis, but they're mostly from the United States and dozens of other countries and employed by companies such as General Electric, Bechtel, Parsons, KBR, Fluor and Perini.

The U.S. military has become one of the prime clients of the industry. Private firms now providing the logistics of every major U.S. military deployment, maintaining strategic weapons systems like the B-2 stealth bomber and Global Hawk unmanned aerial vehicle, and taking over the ROTC programs in over 200 American universities, according to Singer.

From 1994 to 2002, the U.S. Defense Department entered into over 3,000 contracts with U.S.-based military firms, estimated at a value of more than $300 billion. The privatized military industry has several hundred companies operating in over 100 countries on six continents, and over $100 billion in annual global revenue, according to Singer.

Company Breakdown: Not only are large companies like Halliburton, Bechtel and KBR over in Iraq, but so are smaller companies that are trying to rebuild schools, infrastructures and police stations in Iraq while others like McNeil Technologies and Segovia Inc. provide various technological services.

The companies represent logistical support firms, private security operations, and private military companies, the latter being basically private combat forces for hire.

The U.S. Agency for International Development (USAID) awarded the largest of its postwar Iraq contracts to Bechtel to rebuild power generation facilities, electrical grids, water and sewage systems and airport facilities.

The U.S. Army Corp of Engineers awarded Halliburton subsidiary KBR a $10 billion contract to fight oil well fires and reconstruct Iraqi oil fields.

According to the Center for Public Integrity, the top 20 contractors, ranked by total contract value, for activities in Iraq and Afghanistan, from 2002 through July 1, 2004, are:

1. KBR (Halliburton), Houston, Texas: $11.431 billion

2. Parsons Corp., Pasadena, Calif.: $5.286 billion

3. Fluor Corp., Aliso Viejo, Calif.: $3.755 billion

4. Washington Group International, Arlington, Va.: $3.133 billion

5. Shaw Group/Shaw Engineering and Infrastructure, Baton Rouge, La.: $3.051 billion

6. Bechtel Group Inc., San Francisco, Calif.: $2, 830 billion

7. Perini Corporation, Framingham, Mass.: $2.525 billion

8. Contrack International Inc., Arlington, Va.: $2.325 billion

9. Tetra Tech Inc., Pasadena, Calif.: $1.542 billion

10. USA Environmental Inc., Tampa, Fla. $1,542 billion

11. CH2M Hill, Englewood, Colo.: $1.529 billion

12. American International Contractors, Inc. $1.5 billion

13. Odebrect-Austin $1.5 billion

14. Zapata Engineering, Charlotte, N.C.: $1.479 billion

15. Environmental Chemical Corporation, Burlingame, Calif.: $1.475 billion

16. Explosive Ordnance Technologies Inc., Rumson, N.J.: $1.475 billion

17. Stanley Baker Hill, LLC, Muscatine, Iowa: $1.2 billion

18. International American Products, Irmo, S.C.: $628 million

19. Research Triangle Institute, North Carolina: $466 million

20. Titan Corporation, San Diego, Calif.: $402 million

Other companies include: Louis Berger Group, BearingPoint, Creative Associates International Inc., Chemonics International Inc., Harris Corporation, Readiness Management Support LC, DynCorp (Computer Sciences Corp.), Lucent Technologies and EOD Technology Inc., Blackwater Security Consulting, General Electric, Detection Monitoring Technologies and Sealift Inc.

Compiled by FOXNews.com's Liza Porteus