"Despite the concerted efforts of Western intelligence agencies, considerable mystery and intrigue cloaks the financing of contemporary terrorist organizations, especially those originating in the Middle East. The case of al Qaeda is typical. We know more today than we did three years ago about that organization's financial methods and structure, but we have not identified much about its sources of supply and funding. Similarly, much of what we think we know may only be conjecture, or as the quotation from Tom Ridge above suggests - obsolete. The same gap in our knowledge applied to an even greater extent to many of the lesser known but equally violent terrorist groups throughout the region. An often cited estimate places al Qaeda spending at around $30 million per year to sustain itself in the period preceding 9/11. But it is even less clear what al Qaeda needs or expends today. And we still do not know with any precision just how much money al Qaeda raises, or how its funds are allocated. What we do know with some degree of certainty is that terrorist groups such as al Qaeda have traditionally relied on Islamic charities for much of their funding. The same is true for many like-minded terrorist groups throughout the Middle East."
Naval Postgraduate School, Center for Contemporary Conflict: http://www.ccc.nps.navy.mil
Strategic Insights (March 2006,) v.5 no.3