As a global leader of a terrorist group, Osama bin Laden not only has a coterie of devoted followers, but also another key element: lots of money.

No doubt a steady stream of cash fueled the attacks on the World Trade Center and the Pentagon, which bin Laden is believed to have helped plan. After all, the 19 men involved spent tens of thousands of dollars on flight training, rent and airplane trips before the attacks.

So where did the funding come from?

Nobody knows the exact wealth of Osama bin Laden. He is one of the heirs to a fortune from his family's Saudi Arabian construction business. Some observers estimate his personal wealth to be $300 million.

But other experts say bin Laden may be much poorer, arguing that his family most likely has cut off any allowances. "Important sources believe he is running out of money," says Peter Chalk, a policy analyst at the Rand Corp. who focuses on international terrorism and organized crime. "He doesn't have infinite resources."

Financing a Terrorist Network

But bin Laden appears to have developed an effective global money-raising machine. Like a skilled businessman, he has insulated himself from risk by taking money from diverse sources. "I look at bin Laden as the chief financial officer of a very loosely affiliated group of radicals," says Frank Cilluffo, who chairs a committee on combating terrorism at the Center for Strategic and International Studies, a Washington, D.C., think tank. "It's not this monolithic, hierarchical organization."

Because of the group's decentralization, the finances of bin Laden's operations are difficult to trace. In 1999, the U.S. government added his Al-Qaeda group to a list of roughly two dozen financial terrorist organizations believed to directly contribute to terrorism or political violence. In effect, that designation meant that the U.S. could legally freeze Al-Qaeda's assets, which hasn't stopped the organization. It continues to draw money from a vast global network of charities, welfare organizations and even legitimate businesses.

"

Money is primarily channeled through front organizations and through NGOs, offshore bank accounts," says Chalk. "It's not as if money raised in Riyadh is directly transported to bin Laden in Afghanistan and used to buy Kalashnikovs,

a type of assault rifle. There's a very complex paper trail."

Many of these front groups may appear respectable to donors unaware of links to bin Laden. In fact, some groups serve legitimate purposes. In the southern Philippines, for example, Al-Qaeda has bankrolled irrigation development projects, medical supplies and employment bureaus that help Filipinos find jobs.

But in other cases, it is believed that Al-Qaeda uses charitable contributions for its own terrorist training or activities.

Of course, individual donors, including ideological supporters in Saudi Arabia or the United Arab Emirates, also contribute to his cause.

Bin Laden launders this money through construction businesses and other nominally above-board activities. For example, one town in Pakistan is a popular destination for Saudi Arabians who visit it to go on wildlife hunting expeditions. The town also is believed to be a front for bin Laden's organization. The tourists "pump in millions of dollars ostensibly for tourism, and it'sinvested in bank accounts in Pakistan," says Chalk. "People go there and hunt, but they know the money they spend will end up helping bin Laden."

"When you have

the total sum of money broken down and invested in any number of legitimate businesses, it becomes that much easier to hide," Chalksays.

In addition, most sources believe bin Laden's organization is involved in drug trafficking in Afghanistan and elsewhere. If true, such activity is in keeping with the Taliban ruling government in Afghanistan. The government has allowed bin Laden's group to live in the Afghani mountains. The State Department has identified the Taliban as the world's largest opium producer and says the group uses revenue from the trade to fund international terrorism, among other things.

Outside the Law

Just as bin Laden operates outside the law in raising money, he can tap into an unregulated underground system to access those funds. "It's not as if he goes into a bank and opens an account, Osama Bin Laden, Terrorist, Inc.," says Stephen P. Cohen, a senior fellow at the Brookings Institution, a policy think tank in Washington, D.C.

Instead, Cohen says bin Laden undoubtedly relies on an informal system of banking known as

hundi

, common in the Middle East and South Asia. Based on the honor system, this practice channels money through an underground banking system that relies on a network of ethnic, religious and family ties.

But given that bin Laden is believed to have networks in anywhere from 20 to 60 nations, it's likely that some traditional banks have helped him, Cohen says. Plus, he probably has access to money held under the names of associates.

Certainly, he and associates have been careful to avoid drawing attention to their finances. Media reports have pointed out that the band of terrorists who destroyed the World Trade Center and crashed into the Pentagon avoided transferring financial sums in cash in excess of $10,000 -- an evasive practice known as "smurfing." (The name comes from the couriers whomake numerous small bank deposits for money launderers. Such rapid appearances in a variety of places remind some people of the blue cartoon characters.)

Smurfing skirts around the $10,000 limit, at which banks routinely file reports to the Treasury Department, explains Cilluffo of the Center for Strategic and International Studies. Such reports can tip off regulators to patterns of money laundering.

Investigating a Hydra

The decentralization of Al-Qaeda and the fact that many of its organizations are legitimate businesses or charities complicate the job of investigators. Indeed, bin Laden has borrowed a technique from traditional organized-crime networks. "There are many countries, banks, businesses and NGOs, and it's difficult to trace where money is coming from and what it's being used for," says Chalk. "That's one of the ways in which criminal syndicates in general -- not only terrorists -- channel money throughout the world."