The payments totalled USD 66 million in 2013 alone, according to an investigation by the New York Times published yesterday.
While Al-Qaeda's network was first funded by wealthy donors, "kidnapping for ransom has become today's most significant source of terrorist financing," said David S Cohen, the Treasury Department's under secretary for terrorism and financial intelligence, in a 2012 speech.
"Each transaction encourages another transaction."
The organisation has openly acknowledged the windfall, the paper reported.
Al-Wuhayshi said ransom money - reaching around USD 10 million per hostage in recent cases - accounts for up to half his operating budget.
The paper listed more than USD 90 million paid to Al-Qaeda in the Islamic Maghreb since 2008 - by a Switzerland, Spain, Austria, and state-controlled French company and two payments from undetermined sources.
Somalia's Shebab insurgents received USD 5.1 million from Spain, while Al-Qaeda in the Arabian Peninsula received nearly USD 30 million in two payments, one from Qatar and Oman, the other of undetermined origin.
However, last year a former senior French intelligence official told AFP, speaking on condition of anonymity: "Governments and companies pay in almost every case."
"There is always a ransom or an exchange of some sort: money, the release of prisoners, arms deliveries."
The Times article cited former hostages, negotiators, diplomats and government officials in 10 countries in Europe, Africa and the Middle East, and said the payments were sometimes hidden as development aid.
The US and Britain have notably refused to pay to free kidnapped nationals, the paper reported, with the result that just a few have been rescued in military raids or escaped.
