Supporting claims that industry revenues will hit $200 billion (163 billion euros) in 2010, a member of the Stockholm International Peace Research Institute (SIPRI) said the world had been taken largely unaware by the sector’s rise.

As we’re now 2005 at $100 billion, I think this looks like a credible if not a conservative estimate of the industry’s size and scope,” said the researcher, Caroline Holmqvist.

She said that in the 1991 Gulf War, soldiers outnumbered security personnel by 50 to one but that this ratio had dropped to 10 to one by 2004, a year after the start of the war to oust former dictator Saddam Hussein.

”While it’s true the industry has grown tremendously with the war and the occupation of Iraq, events there have also served to make visible a global trend that was already underway,” Holmqvist said.

Private security firms have come under increasing criticism for human rights abuses, like torture at Iraq’s Abu Ghraib prison, destabilizing weak states and emptying armies by offering soldiers lucrative contracts.

In the latest example of their influence, Baghdad’s airport, the only viable way to travel in and out of Iraq, was closed for a day last week over a pay dispute between a British security firm and the Iraqi government.

SIPRI director Alyson Bailes said that the role of the corporate sector in war was growing and companies were now not only providing weapons but also “active services” to forces on the front line as well as in peacetime.”

The business of defense, of war is big business,” she told European parliamentarians and reporters, adding that these companies could affect the outcomes of conflicts.

Their current role, Bailes said, is “only the tip of an iceberg -- the sharp and pointed bit.”

Holmqvist, author of a study on the sector entitled: “Private Security Companies -- the Case for Regulation”, urged the European Union to use its influence as an “international lawbuilder” to push for legislation.

She said the companies should be pushed to respect international law and human rights, to be held accountable for their actions, and have their contracts made more transparent.

”It’s an issue that is not likely to go away,” she said.

Holmqvist called on the EU, the United Nations and the African Union to act quickly because “there’s a gap at present. There’s a kind of window of opportunity.”

”There is insufficient regulation in many countries,” she went on. “It’s a chance to actually look at the harmonization of new laws rather than struggling to harmonize laws after they are in existence.”