Diesel's retail margin widened 52 cents to $1.627 a gallon this month

The diesel retail-wholesale spread is $1.627 a gallon right now, up 52 cents over the past 30 days. If you sell diesel at the pump, you are keeping more per gallon than you were a month ago. Retail diesel is 6.382, up 14.0% on the month and near the top of its 30-day range at the 95 percent mark, with the range running from 3.459 to 6.529. The price went up and the slice you keep went up with it.

Wholesale has not climbed the same way. RBOB gasoline, the wholesale gasoline benchmark, is 3.041, down 5.4% over the past 30 days and sitting low in its own range at the 34 percent mark. The 3:2:1 crack spread, the rough read on refiner margin, is 59.76, down 2.33 for the month. So the refiner side gave back a little while street diesel margin grew. The extra 52 cents came from retail climbing while wholesale did not.

One thing behind the move is supply. Refinery utilization is 92.5%, down 5.6% on the month and at the 41 percent mark of its range. Less product is coming out of the plants than a few weeks ago, which keeps pressure under pump prices even as wholesale gasoline softens.

With runs easing and diesel already near the top of its 30-day range, the pump price could stay firm into next week if utilization does not pick back up. Watch your own rack cost against the street: as long as wholesale stays soft and retail holds, that $1.627 margin may hold too, but a jump in refinery runs could close the gap fast.