Anyone that wants to should be able to buy oil, they just need to pay for it and take delivery. End of problem. I should be able to buy fuel off of the Saudis and cut out all of the middle mambo jumbo. Since oil oil is the same just head down to the dock and pump it off of the next ship.
Nobody is stopping you from buying oil.
People who use large amounts of fuel like to be able to budget for the future. That means having a known price for the fuel they will use in a given time period.
That’s what drives futures markets.