Diesel's street margin is at its widest in a month, up 18 cents a gallon

The diesel retail-wholesale spread is 1.384 now, up 0.183 over the past 30 days. That is about 18 cents more per gallon between what you pay at the rack and what you charge on the street than you were holding a month ago. Diesel retail is up 6.4 percent over the same stretch and is now at the top of its 30-day range, 5.652 against a low of 3.459. Wholesale has not kept pace with the pump, and that gap is the margin.

Gasoline is doing the opposite. RBOB is 2.911, down 12.5 percent over 30 days, and at 15 percent of its range, low 2.756 and high 3.761. So the two big products split hard this month. Diesel margin got fatter while gasoline cost came off. If your volume leans diesel and freight, this was a good month to be pumping it. If you lean gasoline, your street price has room to follow the rack down before customers notice.

One caution on the diesel side. The 3:2:1 crack spread is 57.46 now, down 10.66 over 30 days, so refiners are earning less per barrel of crude they run even as retail diesel margin widens. That tension does not usually hold. When the refiner take narrows and the pump stays high, wholesale diesel often firms up to close the gap, and that would eat into the street margin you are seeing today.

Watch the rack on diesel over the next week or two. With the crack this tight and retail at its range high, wholesale diesel could start climbing to catch up, which may pull that 18-cent margin cushion back toward where it was.