U.S. retail diesel is at the top of its 30-day range at $5.967 a gallon

Retail diesel is $5.967 a gallon, the highest it has been in 30 days and up 13.5% over that stretch. It is at the 100 percent mark of its range, so anyone pricing a load or quoting a fill today is working off the dearest diesel of the month. There is no cheaper print behind you to lean on.

The retail-wholesale diesel spread is $1.30 a gallon. ULSD futures rose 15.2% and retail rose 13.5%, so wholesale climbed a touch faster and retailers still widened their margin. Crude is what pushed everything up: WTI is $100.05, up 20.2% in 30 days and sitting at the 93 percent mark of its own range, with Brent right behind at $104.61. Gasoline is the quiet one here. RBOB is $3.307, up only 4.9% and at the 74 percent mark of its range, so the pressure is on the diesel barrel, not the gasoline barrel, this month.

The refining side tells the other half. The 3:2:1 crack spread is 61.98, down 3.31 over 30 days, so refiner margin on turning crude into product narrowed even as street margin grew.

Watch the crack against crude. WTI is near the top of its range and the crack is tightening, which leaves refiners less room, and if crude keeps climbing it could pull wholesale up faster than retail and pinch that $1.30 street margin back in. For now the diesel margin is working in the retailer's favor, and that is where it is today.