Zack Beauchamp examines the connection between oil and authoritarianism:
Study after study has found that, while discovering big oil deposits doesn’t turn democratic countries with a lot of oil like Norway and Canada authoritarian, authoritarian countries are more likely to stay that way if they’ve got a ton of oil. Of all the bad things that oil does for countries, this is probably the worst and most robustly demonstrated. Think about how long the Saudi monarchy has stuck around, or Russia’s failed attempt to transition to democracy in the 1990s.
“No country with high levels of oil and gas income has successfully become democratic since 1960,” writes Michael Ross, one of the premier scholars of the oil curse. As you can see in his graph on the right, countries that make a lot of money from oil per capita (the bottom-right group of dots) have spent approximately zero time under democratic rule in the past 50 years.
The main reason for the link between oil and authoritarianism, according to Ross and others, is straightforward: oil gives dictatorships money to buy off their citizens, so they don’t have to democratize.