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References to the price of petroleum are usually references to the spot price of either WTI/Light Crude as traded on the New York Mercantile Exchange (NYMEX) for delivery in Cushing, Oklahoma or the price of Brent as traded on the Intercontinental Exchange (ICE, into which the International Petroleum Exchange has been incorporated) for delivery at Sullom Voe. The price of a barrel (which is 42 US gallons or approximately 159 litres) of oil is highly dependent on both its grade (which is determined by factors such as its specific gravity or API and its sulphur content) and location. The vast majority of oil will not be traded on an exchange but on an over-the-counter basis, typically with reference to a marker crude oil grade that is typically quoted via pricing agencies such as Argus Media Ltd and Platts. Other important benchmarks include Dubai, Tapis, and the OPEC basket. The Energy Information Administration (EIA) uses the Imported Refiner Acquisition Cost, the weighted average cost of all oil imported into the US as their "world oil price".

Weekly reports on crude oil inventories or total stockpiles that exist in storage facilities like these tanks, have a strong bearing on oil prices.
The demand for oil is highly dependent on global macroeconomic conditions, so this is also an important determinant of price. Some economists claim that high oil prices have a large negative impact on the global growth.
OPEC, consisting of Algeria, Angola, Ecuador, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela, was formed to maintain the price of oil at a level most beneficial to its membership considered as a whole, and is considered to be a cartel by some observers. [1]