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Well , finally got something , from Oxford energy
https://www.oxfordenergy.org/wpcms/wp-c ... h-2008.pdfit doesn't give me the historical trend but it is an "in depth" paper on crude oil indexes prices linkage
while somewhat dated (2008) its conclusion fit well with subsequent events .
The indexes move in a seamless fashion for sweet/light crude with a large and active futures market
it move with trigger threshold for heavy/sour grades when the market is on a physical purchase basis
this would reflect the technical problem of re-tooling refineries for "dirtier" grades and the lower content of the gasoline cut
[ Rockman is going to love this ]
"Crude oil is of little use before refining and is traded for its final petroleum products that consumers demand. The intrinsic properties of the crude oils determine the mix of the final petroleum products."
"Despite the wide variety of internationally traded crude oils with different qualities and characteristics
(the 2006 International Crude Oil Market Handbook describes more than 160 traded crude oil streams),
many observers consider the world oil market as ‘one great pool’ (Adelman, 1984).
Others argues that oil markets are ‘globalized’ in the sense that supply and demand shocks that affect prices in one region are transferred into other regional markets (Weiner, 1991).
One implication of the globalization thesis is that prices of similar crudes in different markets should move closely together such that their price differential is more or less constant."
This is in contrast to oil markets being ‘regionalized’ in which oil prices of similar qualities move independently to each other in response to shocks. "
"Given the large variety of crude oils traded in the international market, it is important to limit our analysis to few crude streams. we focus our analysis on the following seven types of crude oils imported into the USA:
Nigerian Bonny Light (37º), Algerian Saharan Blend (44º), Mexican Maya (22º), Canadian Lloyd Blend (22º), West Texas Intermediate (40º), Brent (38º), and Dubai’s Fateh (32º). "
the paper anticipate the great reversal of the indexes of 2011
when WTI was CHEAPER than Brent ,
this led to a very sharp drop in demand for the sour crude from Saudi Arabia ,
hence , presumably , their price war .