Valero Energy the largest refiner in the US, buys their product from the producers at the market price. They have a trading division that goes to work at 4 am to start buying crude for their many refineries., so they won't run out of crude. It is a very complicated procedure. The big integrated oil companies like Exxon/Mobile are not subject to the daily whims of the market and so have an advantage.

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Gary
85 300D Ivory, 202,000
Beatus exsisto Jesu, verus et Deus verus Vir