[teaserteam]

 
If you say the 1974 agreement between Saudi and US had nothing to do with currency, then, what had it to do with?   

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Why don't you dig it up and tell us?  My finding is there was an agreement in 1974 for US to buy oil from Saudi.  The agreement is like any other agreement. The currency specified was US dollar and not Saudi Riyal.  "Oil has always traded in non-dollar currencies ... Saudi riyal remains pegged to the US dollar, and its stock of financial assets are dollar-focused."  As Saudi is a country and the oil belongs to Saudi,  how they want to sell their oil to other nations is non of US's business.