Add up all the different buyers' and sellers' guesses about the future of oil (incorporating diffuse knowledge about damage to infrastructure, capacity to rebuild, and intentions of the actors) and (we're told) we'll get a number that accurately reflects the real situation.
And, unlike Pagerank, this number can't be manipulated by flooding the system with spurious, self-serving inputs. If you want to move this price, you have to buy or sell something, which costs money.
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