Cushing, Oklahoma is a pipeline crossroads with a large concentration of crude storage tanks. It has no refinery of consequence, no port, and no local demand worth mentioning. It matters for exactly one reason: it is the delivery point for the WTI futures contract.

That makes Cushing stocks a different kind of number from national inventory. National stocks tell you about the US balance. Cushing stocks tell you about the specific tanks into which a WTI short must deliver and out of which a WTI long must take, which is a statement about the contract rather than about the country.

When Cushing fills, the WTI contract has a problem that national inventory data will not show. A short can always deliver; a long facing expiry with no storage available and no ability to take physical possession is in a very different position, and the price required to induce someone to take the barrel can fall a long way. That mechanism, not speculation, is the mechanical explanation of the April 2020 negative settlement.

WORKED EXAMPLEReading Cushing against capacity

Nameplate shell capacitylarge, and published

Working capacitylower, since tanks need working volume

Contractually committed capacitynot published

Effectively available to the marketlower still, and not observable

Utilisation against nameplate systematically understates how full the hub effectively is

Which is why tank-tops calls tend to be early. The binding constraint is below the published one by an unknown margin.

The general lesson generalises beyond Cushing: a delivery-point inventory series is a property of a contract, and it should be read alongside the contract's own structure rather than folded into a national aggregate. A hub filling while national stocks fall is a coherent and informative state, and an aggregate that averages them away destroys exactly the signal you wanted.

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The Cushing series alongside national crude stocks, so the two can be read separately.