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You don't need to use derivatives to gamble, they control the supply but that control is a lagging control. Any decision they make is essentially a bet about where the oil market is going to move in several months. They are usually big enough that any move they make is going to set the tone but that isn't always the case.

They need to make continual bets on the health of transports, changes in energy mix etc in order to move or keep the price in a favorable band for them. Misstep and the price of oil falls, cutting into their profits or push it too high and face demand destruction and shale extraction coming online because it's profitable at those higher prices, increasing competition and stifling volumes simultaneously.