Diesel's retail-wholesale spread is 25.5 cents wider than a month ago

The gap between wholesale diesel and the street price is 1.639 today, up 0.255 over the past 30 days. If you buy at the rack and sell retail, there is more room in that spread now than a month back, and it is worth checking whether your street price has kept pace with it.

The widening comes as diesel itself is at its 30-day high. U.S. diesel is 6.529, up 15.5 percent over the month, and that is the very top of its range (low 3.459, high 6.529). Gasoline is close behind at 4.61, up 9.3 percent and at the 99 percent mark of its own range. Both fuels are near the most anyone has paid in a month, so replacement cost on your next load is running high.

Crude backs the move. Brent is 96.51 and WTI is 91.16, both up about 8 percent over 30 days and both around two-thirds of their range. Refined product has climbed faster than crude, and that is where the wider street spread on diesel is coming from.

One thing worth watching is the 3:2:1 crack spread, now 56.35 and down 4.98 over the month. That is refiner margin, and it has tightened even while pump prices climbed. If it keeps narrowing, refiners could ease run rates, and that may firm wholesale diesel further from here.