Diesel's retail-wholesale spread is 28 cents tighter than a month ago

The gap between wholesale diesel and the street price is 1.356 a gallon right now, down 28 cents over the past 30 days. Your pump margin on diesel is thinner than it was, and the move came mostly from the cost side rising faster than retail caught up.

Crude is the reason. Brent is 116.72, up 13.2% over the month, and it is sitting at the very top of its 30-day range, the high of 116.72. WTI is 103.27, up 12.1%, at the 92 percent mark. ULSD diesel futures are 4.984, up 4.4% and at 83 percent of range. So the wholesale number you buy at kept climbing while street diesel lagged, and that is where the 28 cents went. Refiners feel the same squeeze from a different angle: the 3:2:1 crack spread is 56.43, down 18.72 over the month, so the margin on turning a barrel into product tightened too.

Gasoline tells the opposite story. RBOB is 3.212, down 10.5% over the month, and it is at the middle of its range, the 50 percent mark. If you run both products, the diesel side is where the cost pressure is, not the gas side.

Natural gas is cheap and heavy on supply. Henry Hub is 2.64, down 12.7% and at the very bottom of its 30-day range. U.S. storage is 3644, at the 100 percent mark of its range, up 8.7%. Full tanks and a soft price, which matters for anyone pricing against heating demand this fall.

If crude holds near the top of its range, street diesel could keep catching up to wholesale over the next week or two, which may give back some of that 28 cents. Watch the retail number more than the futures screen to see when it does.