According to a report by Wealth-X, Sheikh Khalifa's yacht is merely 3.5 per cent of his total net worth of USD 17.9 billion.
This is followed by Oracle CEO Larry Ellison's USD 500 million acquisition of Lanai Island in Hawaii in 2012 at the second place. He was named top billionaire island owner by Wealth-X in June 2013, beating other billionaires such as Google CEO Larry Page and Microsoft co-founder Paul Allen.
As per the Wealth-X report, luxury yachts are the most popular luxury asset acquisition as eight of the ten billionaires in the list own these luxury vessels.
As money for them is no object, these billionaires have "spared no expense in indulging their appetite for luxury assets such as private islands or top-of-the-line superyachts".
Russian tycoon Roman Abramovich's yacht Eclipse has bagged the third position with a valuation of USD 485 million.
"Measuring a whopping 590-feet, Khalifa's Azzam is the biggest yacht in the world, overtaking Abramovich's 533-feet yacht Eclipse, which was the world's biggest for the past three years," the report said.
Besides, Russian vodka tycoon Yury Shefler comes fourth on the list with his luxury yacht Serene, an asset - with a price tag of USD 300 million - representing over 20 per cent of his net worth of USD 1.6 billion.
Andrey Melnichenko's purchase of yacht - A - for USD 323 million is the fifth most expensive luxury asset acquisition.
Wealth-X list of all-time top 10 most expensive billionaire luxury asset acquisitions: