Since World War II, the price of oil has suffered spikes generally correlating with instability in the Middle East. Prices have fluctuated between a $20 to $30 per barrel average during times of relative peace to spikes above $75 during the 1970s and the post-9/11 War on Terror.
The price of oil is subject to a number of different pressures, ranging from simple supply and demand to the political stability of oil producing countries. While the eventual depletion of the world's oil supply guarantees an ultimate increase in the price of oil over time, new discoveries and improved drilling and extraction technologies have so far kept scarcity at bay.
A significant amount of the pressure on oil prices comes from the cartel that controls much of the world's oil production. The Organization of Petroleum Exporting Countries sets production quotas for the oil industry, and raises or lowers production in order to manipulate the price. After the September 11th attacks and the subsequent increase in the cost of oil, American companies began extracting shale oil, which had become profitable due to the rise in price. As these new providers grew in capacity, OPEC began raising production quotas in an attempt to drive the price down and force them out of the market.