It's looked not only at Brent crude but at some other exotic hydrocarbon cocktails - West Texas Intermediate, the Argus Sour Crude Index, Brent Blend or BFOE (the basket of the North Sea's Brent, Forties, Oseberg and Ekofisk), Dubai and Oman, Tapis and Minas, and East Siberia-Pacific Ocean Blend.

BBC: Setting prices crudely