Diesel wholesale is up 13.9 percent in 30 days while the retail spread tightened to $1.104

ULSD futures are 4.417 today, up 13.9 percent over the past 30 days and sitting at the 84 percent mark of the month's range, which runs from 3.093 to 4.677. Diesel moved faster than anything else on the board, and it lands on your diesel buy first. Wholesale is climbing toward the top of its month.

The part that costs you is the retail-wholesale spread on diesel. The spread is 1.104 now, down 0.367 over the same 30 days. So as the cost of the fuel ran up almost 14 percent, the gap between what you pay at the rack and what the street charges got 37 cents a gallon thinner. Your rack cost is chasing the retail price faster than retail is moving, and that lost margin is yours. If you are pricing diesel off yesterday's board, check it again this morning before you set the sign.

Crude backs up the move but does not explain all of it. Brent is 93.71, up 11.9 percent, and WTI is 89.25, up 11.1 percent, both near the middle of their 30-day ranges at 55 and 52 percent. Diesel outran both of them, and the 3:2:1 crack is 60.49, wider by 3.48. Refiners are earning more per barrel on the product side, and the product doing the work is distillate, not gasoline. RBOB is 3.14, up only 5.8 percent and down at the 38 percent mark of its range, so the pressure is on the diesel side of the barrel, not the gas side.

Watch the retail spread from here. If wholesale keeps grinding up and the street holds price, that 1.104 could keep thinning, and diesel margin may stay tight until retail catches up.