[Ronin]

With the demand for gasoline falling overnight and petroleum becoming needed primarily as feedstock for plastics, the US would immediately become self-sufficient in crude oil. What will happen in the Middle East without the huge flow of cash from the Western hemisphere? How will world politics be changed?

Within 10 years all the "cities" in Saudi Arabia would be pretty much ghost towns. As the money runs out, the foreigners who actually do everything to keep the infrastructure running would bail. The royalty would grab whats left of the treasury and book for some villa in Europe... the rest of the populations would go back to living in tents and humping goats.

That, in itself, would be the most wonderful thing I could think of.

[Kevmo]

the rest of the populations would go back to living in tents and humping goats.
***They seem to be halfway there already.