Thailand's king is the world's richest royal, according to a Forbes magazine list dominated by Middle Eastern monarchs riding high on surging oil prices.
Forbes says the 15 monarchs on its list had a combined wealth of $US131 billion, up from $US95 billion last year, adding that they had managed to hold on to their riches "despite controversy ranging from tax evasion to the dissolution of parliaments in Swaziland and Kuwait".
Among European monarchs, Prince Hans Adam II of Liechtenstein is the wealthiest, followed by Prince Albert of Monaco and Queen Elizabeth of Britain.
It did, however, warn that its wealth estimates were "a blend or art and science" because the relationship between individual and state wealth was not always clear.
King Bhumibol, 80-years-old and the world's longest-reigning monarch after six decades on the throne, is regarded as semi-divine by Thais.
Forbes says he is worth an estimated $35 billion.
Bhumibol took the top spot from the only other Asian monarch on the list, Sultan Hassanal Bolkiah of oil-rich Brunei, who fell to the number four slot after his fortunes shrank from a year ago to $20 billion.