Diesel's retail margin fell to $1.015 a gallon, down from about $1.74 a month ago

The gap between what a diesel retailer pays at the rack and what they charge at the pump is 1.015 today, down 0.724 over the past 30 days. Wholesale diesel ran up faster than street prices, and the retail side has not caught up, so the margin on every gallon sold is a good deal thinner than it was a month back.

You can see the wholesale run in the futures. ULSD is 4.181, up 31.6 percent over 30 days, the biggest move on the board, and it is trading at the 78 percent mark of its month-long range between 3.093 and 4.496. Brent is up 31.2 percent and WTI up 27.0 percent, so crude is climbing too, but diesel led the pack. When the rack price rises this fast and pump prices lag, the person absorbing the difference is whoever is selling retail without a pass-through in place.

Refiners are on the other side of that trade. The 3:2:1 crack is 64.3, wider by 9.48 over the past 30 days, so the margin on turning a barrel of crude into product is up while the retail street margin is down. If you buy wholesale and sell retail, this is the month the squeeze landed on your end of the chain.

Diesel is near the top of its range with crude still moving up, so the wholesale cost may hold high or climb further before it eases. If it does, retail prices could keep pushing up just to rebuild the margin that got compressed, which means the pump number a hauler pays looks set to stay firm for now. Worth watching whether street diesel starts closing that gap in the next week.