One-fifth of Saudi Arabian millionaires make their money from oil, said Wealth Insight, 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 Wealth Insight, said in Monday's report.
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.
Prince Alwaleed Bin Talah Al Saud, Saudi's richest citizen with a net worth of $27 billion according to Forbes, fell to 34th place in the rankings in 2015 from 30th last year.
However, Forbes said his wealth has risen from $20.4 billion in March 2014 and $22.6 billion in March 2015.
Turmoil in the Middle East, an unimpressive international stock market debut and tumbling oil prices will hit the wealth of Saudi Arabia's richest in years to come, according to a new report from Wealth Insight.
Over the next five years, more Saudis will become U. dollar-millionaires, but the rate of increase will slow to 12.4 percent, less than half the steep 25 percent rate seen between 20, said the research firm.
This means that by 2020, around 55,245 Saudis will be high-net-worth individuals, with over million in net assets, excluding their primary residence.
This is up from 49,150 in 2015, according to Wealth Insight, when Saudi Arabia—one of the most populous countries in the Gulf—had a total population of around 29 million.
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.
Saudi Arabia hopes for 'activist investors' 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 6.2 billion in 2014.