There is a lot of crude oil left underground. Oil companies quote "reserves" which some people confuse with the actual amount of oil underground, but are more to do with the cost of extracting it by oil wells. Most of the crude left underground is in the Middle East which is not a politically stable part of the world. Some governments with lots of oil reserves work together through OPEC to keep production low and prices high. Politicians in countries that burn much oil complain about high oil prices, because voters complain. However many environmentalists worry about damage being done by using oil as a fuel source (especially global warming) and are therefore happy when prices are kept high so that people use less oil.