Why has U.S. petroleum inventory climbed 6.0% over the past month?

U.S. petroleum inventory is up 6.0% over the past 30 days, now 428.91 million barrels. A build usually comes with softer prices, because more oil in tanks means more supply chasing the same demand. That is not what happened this month, and the gap is worth working out.

The first thing I checked was crude itself. WTI is 89.58, up 11.5% over the same 30 days, with a high of 108.66 and a low of 68.25. Brent is 94.22, up 12.5%, high 112.1, low 71.57. So crude in storage grew while the price of that crude went up. Those two normally pull against each other. When both rise together, something other than plain supply and demand is setting the price.

The inventory number has more to say than its headline. It is 428.91 now, but the 30-day high is 465.729 and the low is 404.508. So the build climbed to well above where it is today and has since pulled back. Current stock is closer to the floor of the month than the ceiling. The barrels piled up, then some of them left. What I am looking at is the tail of a build, not the peak.

So why did crude pile up at all while its price was climbing? Energy Secretary Chris Wright, speaking in Caracas, gave the cleanest version of it. He said new Venezuela deals could raise crude production and push oil prices down, but that "the biggest kink right now in gasoline and diesel prices is refining capacity." Read that against the inventory build and it fits. Crude can arrive faster than refineries can turn it into fuel. When that happens, the raw barrel backs up in storage even as the finished product it feeds gets tighter and dearer. The build is a sign the bottleneck is downstream of the tank farm, at the still.

The product prices confirm which barrel is tight. ULSD diesel futures are 4.446, up 14.7% over 30 days, with a high of 4.677 and a low of 3.093. Diesel moved more this month than crude or gasoline did. RBOB gasoline is 3.141, up only 5.9%, high 3.761, low 2.756. Diesel ran more than twice as hard as gasoline. If refining capacity were the whole story you would expect both products to climb together against backed-up crude. They did not climb together. Diesel is carrying almost all of it.

The crack spread says the same. The 3:2:1 is 60.61, up 3.6 over the month. RBN Energy put the U.S. Gulf Coast 3-2-1 at an average of $65 per barrel in August, more than two and a half times its level a year ago, and pinned the strength on diesel cracks. For a refiner running the right slate, that is a strong margin, and one earned in a hard operating month. The plants that stayed up and cracked barrels into distillate are being paid well to do it. Nothing wrong with that. It is the return for keeping units running when the product is scarce.

Then the question is why diesel specifically. The wire points at two things happening at once, both outside the U.S. Russia banned diesel exports while Ukrainian drone strikes hit its refineries, pulling a large block of middle distillate off the world market. At the same time the Strait of Hormuz seized up. Kpler counted four tanker crossings on a recent Tuesday against a ten-day average of 13, with some vessels running dark. Qatar and the UAE started transferring LNG cargoes ship to ship outside the strait, a rare move. ING's strategists tied record middle distillate cracks directly to the Middle East re-escalation and the Russian export ban. So the tightest barrel in the world right now is diesel, and the reasons are geopolitical, not a shortage of crude. Crude is building. Diesel is the barrel the world cannot get enough of.

For a fuel operator, the diesel retail-wholesale spread shows where this lands: 1.104, down 0.367 over 30 days. Wholesale diesel rose faster than the street price kept up with. The margin between what a retailer pays for diesel and what the pump earns on it compressed by a third or so over the month. When product costs jump this fast, the rack moves first and the sign on the pole lags, and the retailer eats the difference until street prices catch up. Anyone selling diesel has felt that this month whether or not they named it.

What I am sure of: crude built because the constraint is refining, not supply, and the price pressure has moved into diesel because of Russia and Hormuz, not because the barrel in the ground got scarce. What I am less sure of is where it goes. The build has already drawn back off its high, which could mean refiners are catching up, or could mean crude is being pulled toward export. Wright says Venezuelan barrels could more than double production, but by his own account that eases crude, not the refining kink, and it would take years. The tight thing is diesel, and nothing in this month's data fixes that quickly.

And that was just the data. See you tomorrow.