Since September, U.S. commercial stocks have risen by about 22 million barrels.
Assuming all of that fed into tank farms, rather than refineries or pipelines, whose inventory levels generally don't fluctuate much, more than half of the nation's tanks still stand empty, the data show.
The historically large volume of empty tank space may also herald a pause, if not an end, to an unrelenting rout in global markets, as traders embark on a sustained campaign to buy physical crude to stockpile, analysts said -- at least until stocks rise so high that space once again becomes scarce.
"We're at an inflection point" in the oil market, said Philip K. Verleger, an energy economist who has closely tracked oil storage economics for three decades. "Prices can stay at these levels as storage fills. But if demand doesn't pick up or supply go down, then prices will fall again."
The figures may surprise traders who have been thus far focused on the atypical build in stockpiles this winter, with inventories reaching record seasonal highs at a time when they normally decline due to heating demand and year-end tax issues.