... oil finished?

Imagine to wake up one day, turn on the television and discover that the last drop of oil is exhausted. Researches of new deposits failed. The humanity lost its biggest source of energy.

This scenario is not absurd at all. We consume oil at a frightening rate and nature cannot recreate it in time to replace the used one. Unless of finding new deposits, it is estimated that oil will exhaust within a few decades.
It is expected that mankind has other sources of energy from which draw. Even if governments are facing the "exhaustion problem" from some years, there are no guarantees: the natural sources appear at present insufficient, precisely because we realized it too late.

So what would happen if tomorrow we will discover we do not have more oil available?

Probably chaos and panic! Immediately the civilization we know would collapse. The end of oil means the end of transportation, every supply chain required to run a modern society. The trucks that bring the food in our cities would stop, and the cars that transport workers to work would become completely useless. This would immediately shut down most businesses and services. This also includes the army and national guard, because modern militaries are nearly useless without trucks to carry troops, food and medical supplies. But bad news wouldn’t finish, electricity would stop in most locations within some week. At the beginning, maybe, people living in rural areas would be fine, but cities would quickly become uninhabitable and within a couple of weeks all the food in the cities would be exhausted. These desperate hunger people would quickly flood nearby rural areas and overwhelm all available livestock and food stores. To survive people would start again to organize them in small farming communities, and one of the most problem could be armed groups with the aim of stoling food and useful tools. Within 2 years starvation could kill 3/4 of the population in developed nations. Only people living far away from civilization would be relatively safe, aid Ironically, the poorest parts of the developing world would be relatively unaffected.

Of course the immediate loss of oil would definitely cause the end of the world as we know it.