To add to your stat:

One US 42 gallon barrel of crude oil, when refined, produces about 20 gallons of finished motor gasoline, and 7 gallons of diesel, as well as other petroleum products.
http://www.eia.doe.gov/kids/energyfacts/sources/non-renewable/oil.html

So it not last that long really....

I think if your Hyperthetical situation happened in any country (i.e the countries main source of power being taken away) it would collapse into anarchy pretty quickly. There would be riots when people rushed to buy up any left over oil and the economy would pretty much grind to a halt if it lasted for an extended period of time. I dont know if one week would be long enough to have a massive effect but it would cause panic both on the streets and on the Stock Markets. We had a similar situation over here in England not so long ago where the petrol prices went up so high, it prompted people to form road blocks in protest, stopping the fuel trucks from supplying the petrol stations. It was bedlam for a while with people stock piling petrol whenever they could.

People panic. It is in our make up. We see the worst case scenario and go of the deep end.