This means that by 2020, around 55,245 Saudis will be high-net-worth individuals, with over $1 million in net assets, excluding their primary residence. This is up from 49,150 in 2015, according to WealthInsight, when Saudi Arabia—one of the most populous countries in the Gulf—had a total population of around 29 million.
One-fifth of Saudi Arabian millionaires make their money from oil, said WealthInsight, but the 50 percent decline in the price of WTI crude oil over the last 12 months is only one factor behind the upcoming slowdown.
"There have been other worries among the Kingdom's wealthy," Oliver Williams, head of WealthInsight, said in Monday's report.
"The collapse of the oil price is only half of the picture. So far, 2015 has seen the Kingdom's stock market make its disappointing debut on the world stage, two wars have been commenced along its borders and there is a new prospect of economic rivalry with Iran."
Saudi Arabia's Tadawul stock exchange officially opened to foreign investors on June 15 amid a great degree of hype. However, tight regulations and high valuations meant that foreign buyers failed to materialize in substantial volumes, while domestic investors sold. The benchmark Tadawul All Share Index has fallen by roughly 5 percent since then.
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Saudi Arabia's economic growth slowed from a peak of 10 percent in 2011 to 3.5 percent last year. The country is designated "high income" by the World Bank, with gross domestic product (GDP) of $746.2 billion in 2014.
Saudi Arabia's richest citizens have fallen this year in Forbes' list of the world's billionaires, particular those that are heavily invested in oil.