I thought it would be interesting to convert the amount of oil consumed by the world each year into cubic kilometres to give a sense of scale of how much oil we use and how much could possibly be left. The world consumes about 80 million barrels of oil a day. Each barrel is 159 litres and a cubic kilometre corresponds to 10^12 litres, so the amount of oil the world consumes in a year is equivalent to 4.6 cubic kilometres. This would correspond to a cubic pit with sides that are about 1.45 km long. The US consumes a little over a quarter of the world's oil, which is about 1.2 cubic kilometres. The Arctic National Wildlife Refuge is estimated to have about 10 billion barrels of recoverable oil, about a half of year's supply.
Proven world reserves amount to about 1.3 trillion barrels of oil or about 200 cubic kilometres. If we continue at current rates of consumption, then we have about 40 years of oil left. If the rest of the world decided to use oil like American's then the world's yearly consumption could increase by a factor of 5, which would bring us down to 8 years worth of reserve. However, given that the surface of the earth is about 500 million square kilometres, it seems plausible that there is a lot more oil out there that hasn't been found, especially under the deep ocean. The main constraint is cost and greenhouse gas emissions. We may not run out of oil anytime soon but we may have run out of cheap oil already.