Oil moves violently because almost nothing about it responds to price in the short run. A demand elasticity near −0.06 and a supply elasticity near 0.04 mean a 5% loss of supply needs something close to an 85% move in price to clear the market, where fresh tomatoes would need about 1%. That is why a weekly American stock survey moves a global benchmark, and why it is worth taking apart. The headline everyone quotes — crude stocks fell 4.4 million barrels — is one line of a six-term identity, and which term moved is the entire question: a draw built on hard refinery runs is a different market from one built on collapsed imports, and the two point opposite ways. So the components below are drawn with their signs, the change they imply is checked against the change actually reported, and the barrels the identity cannot place are shown rather than quietly absorbed. Stocks are then read as days of cover rather than as a barrel count, because refining capacity has grown and the same barrel no longer buys the same comfort.