When discussing crude oil prices, we will encounter some standard units: (1) Europe’s Brent (the name comes from a North Sea oil field) crude oil price; (2) the United States uses WTI (West Texas Intermediate, West Texas Intermediate crude oil) crude oil price; (3) Dubai crude oil price in the Middle East. All other crude oil prices are set on this basis, and the price also depends on the quality of the crude oil (density, sulfur content, etc.). Crude oil prices are measured in US dollars/barrel; petroleum product prices are expressed in US dollars/ton; natural gas product prices are expressed in US dollars/million British thermal units. To simplify, crude oil price means Brent crude oil price, which is the benchmark price for all oil imported into Europe. However, when talking about long-term oil prices, it is important to know whether they are nominal or dollar prices, or real or constant dollar prices. The former is the price paid at that time, and the latter is the actual price after eliminating the factors of changes in the purchasing power of the US dollar in long-term transactions. Because the price proposed in a transaction for the ratio of petroleum fuel to oil barrels fluctuates, actual transaction prices can vary widely. The reference for oil prices is often the retail price of WTI/light crude oil exported to Cushing, Oklahoma on the New York Mercantile Exchange (NYMEX) in the United States, or the export price traded on the Interstate Exchange (ICE). Brent crude oil prices in Salom Bay, where the International Petroleum Exchange is integrated with ICE. The price of a barrel of crude oil (US gallon or approximately 159 liters) is highly dependent on its grade (determined by density or API degree and sulfur content) and its origin. The vast majority of crude oil is not traded on exchanges, but is mostly traded on the basis of cross-border sales, mostly based on crude oil grades determined by pricing agencies such as Argus Media Ltd and Platts as the reference standard. Some other important benchmarks include Dubai prices, Malaysian Tapis light crude prices and OPEC basket prices. The U.S. Energy Information Administration uses the Imported Refiner Acquisition Cost, the average price of all oil imported into the United States, to calculate world oil prices.