Diesel's retail-wholesale margin is $1.067 a gallon, near the top of its 30-day range

The diesel spread between wholesale and street is 1.067 today, up 0.095 over the past 30 days. That is about a dime a gallon wider than a month ago, and it is the number that matters most for anyone selling diesel right now. If you move any real volume, that widening covered a lot of ground while you were watching other things.

The two main fuels split this month, and they split hard. Diesel is 5.257, up 9.6% over 30 days, and it is at the 82 percent mark of its range. RBOB gasoline went the other way: 2.904, down 12.0%, sitting at just the 15 percent mark of its own range. So diesel is near its month high while gasoline is near its month low. Wholesale gasoline is cheap right now, and any margin you are holding on the gas side came from the pump not dropping as fast as the rack. The diesel side is where the dollars are, both on price and on the spread.

One thing cuts against the diesel story. The 3:2:1 crack spread is 57.23 now, down 10.87 over 30 days, so refiner margins tightened by a good chunk this month. The crack spread is the barrel economics behind your rack price. When it compresses, it can eventually push wholesale diesel up faster than retail, which would pinch the same 1.067 spread that looks good today.

On the gas side, natural gas is quiet. Henry Hub is 2.733, down 6.5%, at the 26 percent mark of its range, so nothing there is forcing your hand.

Watch the diesel retail-wholesale spread over the next week; with the crack spread tightening, some of that extra margin could come back.