In their meetings with Gulf and Western officials these days, members of the Syrian opposition have a key message: the extremists are winning the battle for recruits.

“Of course everybody’s looking for funding,” said a senior opposition delegation member at the recent Manama Dialogue security conference, an annual forum on regional security challenges in the Gulf. “There are people in the Gulf and in the region who support this kind of [extremist] movement. . . . We’ve been warning for more than a year that our competitors on the ground, they are providing bakeries, education, many things.”

Over the last two and a half years, private Gulf donations have likely reached into the hundreds of millions of dollars—much of this money channeled to groups that are operating outside the Western-backed Supreme Military Council, the command structure of the rebel Free Syria Army. In a recent paper for the Brookings Institution, I chart how these donations began, how private backers influenced the creation and ideology of rebel brigades, and how these Gulf-based patrons helped fracture the military opposition.

One of the most elusive questions around these donations, however, is simply how they arrive— and understanding the logistics is key to any efforts to cut off the funds to extremist-linked groups. How does a willing donor in the Gulf channel his funds from Kuwait, Saudi Arabia, Bahrain, or elsewhere straight to a rebel brigade in war-torn Syria?

Collecting Donations

There are two stages to the donation process, the giving and the receiving. For much of the Syrian conflict, Kuwait has served as a clearinghouse. The tiny Gulf country of just over 3 million lacked a counterterrorist financing law until just this summer, and the new legislation has yet to be fully implemented. Donors have taken advantage not just of Kuwait’s poor legal framework but also of its pluralistic political environment, where free assembly and private charities are permitted.

Donors in Kuwait—many of whom are high-profile clerics and politicians—often solicit donations on social media, but they collect them in person. Former members of parliament and clerics have opened their diwaniyas, spaces used for gathering to talk politics, for donations. Large tribes have held days-long events that mimicked telethons in their dramatization. Borrowing a marketing strategy of humanitarian NGOs, they earmarked specific amounts for their buying potential. Eight-hundred dollars would buy a rocket-propelled grenade, for example, or $2,500 would arm one fighter for battle. Some well-known individuals also used Syrian expatriate liaisons to visit wealthy potential donors in a door-to-door fashion, requesting charity.

Despite facing increased government and international scrutiny, bank transfers are also an option. Deposit instructions were once published publicly but are now available on request. Donors provide numbers using WhatsApp, a mobile messaging app, through which they can message account and transfer information to patrons.

And If You’re Not in Kuwait?

For those outside of Kuwait, things are only slightly more complicated. In the early days of the conflict, Gulf citizens could simply transfer their donations to individuals in Kuwait, who would then take care of getting them into Syria. Although some countries have tightly regulated donations directly into Syria, it is more difficult to track such funds when they move through Kuwait. This is the case with Saudi Arabia, which has strong business and personal ties to Kuwait. In some cases, Kuwaiti donors have also designated representatives in other Gulf countries who are authorized to collect funds on their behalf. This allows individuals to provide funds without the risk and scrutiny associated with international transfer.

Other Gulf residents came to Kuwait directly with their funds. Until Kuwait’s new anti-terror law was passed this summer, customs agents couldn’t stop passengers carrying cash—and many did just that.

Getting Past the Syrian Border

Once the money is gathered in Kuwait, it is a more difficult task to move it into Syria—as much because of Syrian government scrutiny as because of Gulf countries’ concerns. Large incoming transfers are often flagged for the regime by transfer agents, Syrian expats in the Gulf say, meaning that even personal remittances are often broken up into batches and sourced through various individual recipients.

It’s more likely that donors depend on hawala agents—traditional moneylenders who operate much like a small-time Western Union or other transfer service, sending money from individual to individual—although cash rarely crosses borders. Rather, these transactions are based on trust and often tribal connections. Dealers tally their exchanges, which usually balance as cash crosses from one beneficiary to another.

Deficits are often made up with cash payments, with money carried across the border. This is increasingly how the money moves, likely from Turkey into Syria’s north, with countless middlemen along the way.

Donations in kind once easily moved over the border from Kuwait, often in private buses paid for by donors. In the early days, the route was clear-cut: through Saudi Arabia and Egypt and into Syria’s east. Today, such transfers have all but halted and must navigate a far more difficult obstacle course—Saudi Arabia to Jordan to Egypt, then by sea to Turkey and from there into Syria.

Increased scrutiny of all these pipelines has had the unfortunate effect of making them increasingly less transparent. Donations are split into smaller slices, sent to different cities in Syria, then moved on the ground and routed through growing numbers of intermediaries. Bank transfers are fading in popularity, replaced by cash. Many Kuwaiti donors continue to travel to Syria themselves to meet—or even fight with—the forces they are backing.

As the Syrian conflict continues and grows more disparate, this trend will likely only continue. Many of the donors involved in sending money to Syria have a reputation in Kuwait of having worked in this business for years, so they know the tricks and have strong networks throughout the region.

Elizabeth Dickinson is Gulf correspondent for The National and author of "Playing with Fire: Why Private Gulf Financing for Syria's Extremist Rebels Risks Igniting Sectarian Conflict at Home," a report for the Brookings Institution's Project on U.S.-Islamic World Relations.