You're assuming that they can control the price. It would be simply stupid to sell something for $65 when you could sell it for $90. But if they need x amount of total dollars, they will sell how ever many barrels at $65 to reach that number. At $65 they can still cover costs, and they have endless reserves. At worst, they are selling something cheaply today that they could get a better price for if they held out. Other producers are not in that position which can destabilize many parts of the world.