[fastball]

Just taking Saudi as an example, the oil is owned by the Royal Family, who then use the proceeds to pay for basically all government expenditures (taxes are very low in SA – for example there is no income tax).

When the price is below $40/barrel, they can no longer pay for these services effectively, which obviously causes immediate problems, but in the long term will make it harder and harder for the Sauds to maintain control of an ever-more-disgruntled populace.

I feel like this was made pretty clear in the article.