Slate's Explainer: Why a 'Barrel' of Oil? As the price of a barrel of oil continues to hover at record levels, Slate contributor Daniel Engber explains why a "barrel" was set at 42 gallons -- and how oil really isn't shipped in barrels any more.

Slate's Explainer: Why a 'Barrel' of Oil?

Slate's Explainer: Why a 'Barrel' of Oil?

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As the price of a barrel of oil continues to hover at record levels, Slate contributor Daniel Engber explains why a "barrel" was set at 42 gallons — and how oil really isn't shipped in barrels any more.