<P> In the US, in the states of Arizona, California, Hawaii, Nevada, Oregon and Washington, the Western States Petroleum Association (WSPA) represents companies responsible for producing, distributing, refining, transporting and marketing petroleum . This non-profit trade association was founded in 1907, and is the oldest petroleum trade association in the United States . </P> <P> In the 1950s, shipping costs made up 33 percent of the price of oil transported from the Persian Gulf to USA, but due to the development of supertankers in the 1970s, the cost of shipping dropped to only 5 percent of the price of Persian oil in USA . Due to the increase of the value of the crude oil during the last 30 years, the share of the shipping cost on the final cost of the delivered commodity was less than 3% in 2010 . For example, in 2010 the shipping cost from the Persian Gulf to the USA was in the range of 20 $/ t and the cost of the delivered crude oil around 800 $/ t . </P> <P> After the collapse of the OPEC - administered pricing system in 1985, and a short - lived experiment with netback pricing, oil - exporting countries adopted a market - linked pricing mechanism . First adopted by PEMEX in 1986, market - linked pricing was widely accepted, and by 1988 became and still is the main method for pricing crude oil in international trade . The current reference, or pricing markers, are Brent, WTI, and Dubai / Oman . </P> <P> The chemical structure of petroleum is heterogeneous, composed of hydrocarbon chains of different lengths . Because of this, petroleum may be taken to oil refineries and the hydrocarbon chemicals separated by distillation and treated by other chemical processes, to be used for a variety of purposes . The total cost of a plant is about 9 billion dollars per plant . </P>

When did the most deposits with petroleum form