RBCThis chart from RBC Capital Markets' Helima Croft shows the proven oil reserves for the big oil-producing countries around the world.
Despite Saudi Arabia's huge reserves, RBC writes that "a policy of keeping prices low for the prolonged period needed to put US shale producers out of business would essentially eliminate the country's reserves. According to the IMF, if oil prices fall $25 below the Fund's $100-$105 reference case, with no spending adjustment, Saudi government reserves will be entirely depleted by 2018."
If the Saudis are screwed by 2018, every other country on this list that relies heavily on oil revenue to balance its budget is probably going to see reserves depleted before then.