>> * In 1974, Washington and Riyadh struck a deal by which Saudi Arabia could buy US treasury bills before they were auctioned. In return, Saudi Arabia would sell its oil in dollars—not only enlarging the currency's liquidity but also using those dollars to buy US debt and products.*

> So in exchange to gaining access to US treasuries (debt) before action, they had to buy US treasuries?

I have no knowledge about this besides what's been written in this thread, but I assume that having the ability to buy before the auction means they get a good deal.