Tatiana Serafin 08.20.08, 11:00 PM ET
Earlier this year, Nepal voted to eliminate its 240-year-old Hindu monarchy, and former king Gyanendra was forced to turn over his royal palace in Kathmandu, which has become a museum.
So far the 15 rulers on our list have held on to their riches, despite controversy ranging from tax evasion to the dissolution of parliaments in Swaziland and Kuwait. As a group, the world's 15 richest royals have increased their total wealth to $131 billion, up from $95 billion last year.
At the top of our list is Thailand's King Bhumibol Adulyadej, whose $35 billion estimated net worth is up sevenfold as a result of increased transparency of his Crown Property Holdings. He takes the top spot from the only other Asian monarch on the list, the Sultan of Brunei, worth $20 billion, one of only two rulers worth less than they were last year. The sultan, who inherited the riches of an unbroken 600-year-old Muslim dynasty, has had to cut back on his country's oil production because of depleting reserves.
The other loser was Morocco's King Mohammed VI, now worth $1.5 billion, down from last year's $2 billion. A serious drought has slowed the country's economic growth to 2%.
No such problems for the six rulers from Middle Eastern countries, who have been raking in cash, largely from oil. The region's richest, Abu Dhabi's Sheikh Khalifa Bin Zayed Al Nahyan, comes in again at No. 2 on our list, with an estimated net worth of $23 billion. Abu Dhabi is home to 95% of the United Arab Emirate's oil deposits, the source of the Sheikh's wealth. The tiny emirate is also making news because of high-profile investments by its state-owned investment vehicle including a $7.5 billion investment in Citibank.
Dubai's Sheikh Mohammed bin Rashid Al Maktoum, with a net worth of $18 billion, is the majority shareholder of Dubai Holding, which has investments in companies such as Sony (nyse: SNE - news - people ) and defense contractor EADS. His country's investment fund recently paid $5 billion for a stake in MGM Mirage (nyse: MGM - news - people ) and $825 million to purchase retailer Barneys New York.
Things are thornier for Prince Hans-Adam II of Liechtenstein, sixth on our list with an estimated net worth of $5 billion. A major source of his net worth, LGT bank, which his family has run for 70 years, is the focus of a tax evasion scandal for allegedly helping wealthy clients hide their money. A U.S. Senate investigation claims that his brother, Prince Phillip, met with suspected tax dodgers in his role as LGT chairman.
The last remaining bachelor among these wealthy royals, Prince Albert II of Monaco, is rumored to be putting his girlfriend through French immersion classes. His net worth is estimated to be $1.4 billion and includes high-priced real estate and a stake in a casino in the tiny principality. He is planning to extend the nation, the size of New York's Central Park, by building a new district out into the sea that will be erected on giant pillars. Environmentalists are concerned.
Meanwhile, succession planning is the talk of the town with the two queens on our list. The Netherlands' Queen Beatrix, ranked 14th, is rumored to be considering abdicating in favor of her son, while the U.K.'s Queen Elizabeth, ranked 12th, plans to keep on ruling, thwarting the hopes of her son Prince Charles to get a shot at the throne any time soon.
The only ruler who doesn't preside over a geographic territory is the Aga Kahn; he is the spiritual leader of the world's dispersed 15 million Ismaili Muslims. The equestrian, whose net worth is estimated at $1 billion, recently purchased a stake in Britain's largest horse auction house.
Keep in mind that the wealth of the royals comes from inheritances or positions of power; it is often shared with extended families and often represents money controlled by them in trust for their nation or territory. For these reasons, none of the 15 royals on this list would qualify for our annual ranking of the world's billionaires, regardless of their net worth.
Because of technical and idiosyncratic oddities in the exact relationship between individual and state wealth, these estimates are perforce a blend of art and science.
For instance, Swaziland's King Mswati III is the beneficiary of two funds created by his father in trust for the Swazi nation. While he holds power he has absolute discretion over use of the income, which has allowed him to build palaces for each of his 13 wives and throw himself lavish birthday parties, including his recent one celebrating his 40th birthday at a reported $2.5 million cost.
In the U.K., however, royal items such as Buckingham Palace and the British crown jewels are considered to belong to the British nation, not Queen Elizabeth, and as such are not counted in her net worth. Instead, her wealth is derived from property in England and Scotland, fine art, gems and a stamp collection built by her grandfather.
While we have tracked the fortunes of a few high-profile royals, like the Queen of England and Sultan of Brunei, for years, this is only the second time we have published a definitive list of the richest royals. Monarchs of such countries as Spain and Japan failed to make the cut.