Prime Minister John Key has been ranked in a list of the top 20 wealthiest leaders in the world which includes other fortunes made on oil, property and corruption.

The Independent in London ranked Mr Key 18th with $52 million, behind Italian Prime Minister Silvio Berlusconi, (fifth, $12.5 billion), the Queen (13th, $625 million), and Australian Prime Minister Kevin Rudd. (17th, $85 million).

Thailand's King Bhumibol Adulyadej, 82, topped the list with $41.65 billion, ahead of the Sultan of Brunei, who was so fond of spending it up that he had Michael Jackson perform at his 50th birthday.

Others on the list have also let their money go to their head. King Abdullah of Saudi Arabia is having a city constructed and named after him - King Abdullah Economic City.

King Mswati II of Swaziland (16th, $141 million) uses state wealth to bolster his own, and each of his 13 brides has a palace, a retinue and a BMW. The Independent followed the declaration of financial interests of US President Barack Obama, which revealed the value of his recently acquired pooch - $2329.

Mr Key earned his fortune as an investment banker before entering politics.

The Register of Pecuniary Interests, which requires MPs to list their financial holdings, shows that Mr Key owns six properties, including in London, Hawaii and Rodney.

He holds shares or bonds in a ski resort in Aspen, Colorado, and the Bank of America. He sold his shares in mining company Cauldron in February.

Land, property, oil and gas are frequent features of the assets of those on the list.

Prince Albert II of Monaco (ninth, $1.46 billion) includes among his assets the Societe des Bains de Mer, which owns Monaco's casinos.

President Teodoro Obiang Nguema Mbasogo of Equatorial Guinea (12th, $833 million) took $500,000 for himself from the national treasury in 2003 to "fight corruption".

1. King of Thailand: $41.6b

2. Sultan of Brunei: $28.1b

3. Khalifa bin Zayed President of the UAE: $25b

4. King of Saudi Arabia: $23.9b

5. Silvio Berlusconi, Italian Prime Minister: $12.5b

17. Kevin Rudd, Prime Minister of Australia: $85m

18. John Key, New Zealand Prime Minister: $52m