Street diesel margin is $1.104, down 37 cents in a month

The retail-wholesale spread on diesel is $1.104 a gallon, down 37 cents over the past 30 days. Pump diesel is near a monthly high at $5.599, at 98 percent of its 30-day range, so the price your customers pay went up while the cut you keep on each gallon got smaller.

Wholesale is what moved. Diesel futures are $4.54, up 19.6 percent over the same 30 days, while retail diesel rose only 4.7 percent. Your cost per gallon climbed more than four times faster than what you could add at the pump, and that gap is the 37 cents that came out of the spread.

Crude did most of the pulling. WTI is $91.48, up 21.6 percent in 30 days, and Brent is $96.28, up 21.2 percent, both around the middle of their ranges at 57 and 61 percent. Gasoline stayed calmer: RBOB is $3.215, up 13.2 percent, at 46 percent of its range, so the diesel side is carrying the stress right now.

Refiners are on the other side of it. The 3:2:1 crack spread is 62.09, wider by 4.68 over the month, so the margin is good at the rack even as it tightens on the street.

Watch ULSD futures. They are at 91 percent of their 30-day range, near the top, so wholesale diesel could keep climbing. If it does and retail lags again, the street margin may compress further before it recovers.