Diesel is at the top of its 30-day range at $6.529, and street margin is the widest it has been in a month

Diesel is priced at $6.529 today, the very top of its 30-day range and up 15.5% over the past month. The retail-wholesale spread stands at $1.639, so the gross margin between what a station pays and what it charges for diesel is the widest it has been in 30 days. If you sell diesel at retail, that is money in your pocket right now. If you buy it to run trucks, it is the opposite, and the pain is not letting up.

Gasoline tells the same story from a different seat. At $4.61 it is at the 99 percent mark of its own 30-day range, up 9.3%. Both pump products are pinned at the ceiling of their month. Crude is high but has more room below it: WTI is at $94.93, the 71 percent mark of its range, and Brent is at $99.75, the 76 percent mark. The finished fuels are running harder than the barrel they come from, which is why the street spread is fat.

The one crosscurrent is on the refining side. The 3:2:1 crack spread, the refiner's margin on turning a barrel into gasoline and diesel, is 60.52, down 14.79 over the past 30 days. It has tightened even while retail margins widened. Refiners are keeping less of each barrel than they were a month ago, and they tend to defend that number.

Watch the crack spread. If it keeps tightening, refiners could pull back runs or push rack prices up to protect margin, and either move would land on your wholesale cost before it shows at the pump. For now, diesel and gasoline retail margins are as good as they have been in a month, so price your street accordingly while the spread holds.