Oil benchmarks provide a useful way for oil traders and speculators to know which type of oil they are trading. Oil from different fields varies in value thanks to its use in different industries, and varying ease of transport.
Brent crude is the most traded of all of the oil benchmarks, and is defined as crude mostly drilled from the North Sea oilfields: Brent, Forties, Oseberg and Ekofisk (collectively known as BFOE). This oil type is widely used as it is both sweet and light, making it easy to refine into diesel fuel and gasoline. That, and its relative ease of transporting being produced at sea, make it so widely traded.